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National Aeronautics and Space Administration
S p a c e Te l e s c o p e S c i e n c e I n s t i t u t e
S U M M E R 2 0 1 0 V O L 2 7 I S S U E 0 1
Newsletter
Chronology
When the Cycle 18 Call for Proposals was released on December 9, 2009, Cycle 17 was well underway, and the newly installed—as well as the prior-generation—instruments on Hubble had been
calibrated and characterized after Servicing Mission 4. Unlike the situation during the previous Call for Proposals, astronomers could prepare their proposals and estimate resources knowing the instruments were in place and had already been checked out. The Advanced Camera for Surveys (ACS), Cosmic Origins Spectrograph (COS), Fine Guidance Sensor (FGS), Space Telescope Imaging Spectrograph (STIS), and Wide Field Camera 3 (WFC3) were all close to nominal operation and were available for Hubble observing proposals in Cycle 18. The Near Infrared Camera and Multi-Object Spectrometer (NICMOS) was available for proposers as well. However, when the Call for Proposals was issued, the NICMOS cooling system had not yet been restarted, and NICMOS was inactive. The decision on when the cooling system would be restarted had not yet been made. Nevertheless, the proposers were advised to assume NICMOS would be available during Cycle 18.
The Phase 1 deadline for Cycle 18 was February 26, 2010. While some proposals were received well in advance of the deadline, most proposals arrived on the very last day, with an ever-increasing number piling up during the final minutes before 8 p.m. Eastern time. As many astronomers living on the East Coast may remember, that particular day was one of many when snowstorms hit the area and caused a snow emergency. The Institute was actually operating under liberal leave on February 26. Luckily, with the help of our dedicated staff, the proposal submission process was completed without major hiccups. In the end,
we received 1,051 proposals. The final tally was not known until a few days after the deadline because of duplicate submissions and some withdrawals.
Peer Review ProcessHubble proposals are reviewed by members of the international astronomical
community, who serve on various panels organized by science category and proposal size. Large proposals in all science categories are reviewed by the time allocation committee (TAC). All other programs are assigned to panels according to their science category.
The process of selecting the panelists begins with the selection of the Chair about six months prior to the proposal deadline. Neta Bahcall (Princeton) served as Chair of the Cycle 18 TAC. Next, we selected the chairs of the panels, who also serve as members of the TAC. In addition, there are three at-large TAC members, with broad expertise, who review proposals as assigned. The recruitment of panel members is usually completed about two months prior to the proposal deadline. The goal is to have a healthy mix of experienced, senior panelists, as well as younger panel members, at the postdoctoral level. Other important considerations are gender balance and representation of ESA and other countries. For Cycle 18, we anticipated high proposal pressure, and initially invited ~130 scientists from the community as panelists or TAC members. In the event, the proposal pressure exceeded expectations, and additional panelists were recruited—and a new panel constituted—after the Phase Ι deadline. The final Cycle 18 assessment process involved close to 150 panelists and TAC members, which is the largest number ever to participate in a Hubble proposal review.
In order to minimize the workload for each panelist, we increased the number of panels from 12 in Cycle 17 to 14 in Cycle 18. Of these, two panels were for the solar system and exoplanets, two for cool stars and star formation, three for hot stars and stellar populations, three for galaxies, two for active galactic nuclei (AGN) and the intergalactic medium (IGM), and two panels for cosmology.
Each topical set of panels served as “mirrors,” so that proposals could be transferred to a mirror panel if necessitated by conflicts.
National Aeronautics and Space Administration
Claus Leitherer, [email protected], and Daniel Apai, [email protected]
Continuedpage 2
Hubble Cycle 18 Proposal Selection
HH 901 and HH 902 in the Carina NebulaCredit: NASA, ESA, and M. Livio and the
Hubble 20th Anniversary Team (STScI)
2
Hubble Cycle 18from page 1
Ideally, one would like to have all panels be of equal size, but in practice this was not feasible, because different science categories have varying numbers of proposals. In addition, the meeting room sizes vary and impose a limit on the panel size. In Cycle 18, the panels had between 8 and 13 members; the TAC totaled 18.
The proposal review took place during the week of 17–21 May, 2010. As in Cycle 17, we held the Cycle 18 proposal review in the buildings of the Institute and the Physics & Astronomy department of the Johns Hopkins University (JHU). JHU kindly offered the additional space. Most panelists preferred the campus location to the offsite conference center where we held the review in some of the previous years.
The TAC and the panels in Cycle 18 had 2,600 orbits available for allocation. Of these, 2,000 were made available to the panels, and 600 to the TAC. This allocation is smaller than in the previous cycle, due to the allocation of orbits to the (1) Multi-Cycle Treasury Program, (2) remaining COS GTO orbits, and (3) unexecuted Cycle 16 and 17 programs. The oversubscription ratio was 9:1 by orbits, which translated into a proposal acceptance rate of one out of six.
The acceptance rate for archival research was about one out of three, similar to the long-term average.Quite a few observing proposals fell into the medium category (40–99 orbits), making them quite
expensive, but still too small to fall into the large category (100+ orbits). In prior cycles, a “subsidy” was given to medium proposals, meaning that—if such a proposal were approved—the panel would be charged fewer orbits than the number requested. The subsidy is taken from a central pool. In Cycle 18, because of the large oversubscription and the relatively smaller number of orbits available to the panels, there was a concern that—even with the subsidy available—the panels would be hesitant to support any of the medium proposals. To guarantee the approval of at least some scientifically outstanding, medium proposals, 300 orbits from the panel allocation were set aside for them, in lieu of a panel subsidy. Out of this pool, the panel chairs of each set of mirror panels could allocate orbits to their top-ranked medium proposals. We have requested feedback from the panelists on the merits of this approach, in order to develop the process to be used for Cycle 19.
Our policy for handling conflicts of interest remained unchanged from Cycle 17, when we defined co-investigators (CoIs) who are close collaborators to be minor conflicts. Similarly, institutional conflicts were considered to be minor. When a minor conflict arises, the panelist may, at the chair’s discretion, participate in the proposal discussion—but must not cast a vote. Striking a balance between minimizing conflicts of interest and maximizing the expertise of a panel is becoming increasingly challenging as collaborations expand and proposals grow in size. We found our rules led to a healthier discussion in the panels, with no evidence for bias.
StatisticsThe 1,051 proposals submitted in Cycle 18 included 872 general observer (GO), 51 snapshot (SNAP),
75 archival, 10 legacy archival (AR), and 43 theory programs. Six hundred orbits were made available for proposals reviewed by the TAC, and 2,000 for the proposals reviewed by the 14 panels. Three hundred out of 2,000 orbits were reserved for medium-sized proposals (see table with summary of Cycle 18 results). The Cycle 18 panels and TAC recommended approving 196 programs, including 146 GO, 3 SNAP, 28 AR and legacy archival, and 13 theory programs. The recommended theory programs include one GO and five AR calibration programs. Two joint Chandra–Hubble, two joint National Optical Astronomy Observatories–Hubble, and one joint Spitzer–Hubble programs were awarded time by the panels.
Eight large and treasury programs were recommended by the TAC.As a reflection of Hubble’s new capabilities, Cycle 18 has seen one of the highest oversubscriptions
Summary of Cycle 18 Results
Proposals Requested Approved % Accepted ESAAccepted ESA % Total
General Observer 872 146 16.7% 30 20.5%
Snapshot 51 9 17.6% 3 33.3%
Archival Research
75 26 34.7% 0
AR Legacy 10 2 20.0% 0
Theory 43 13 30.2% 0
Total 1,051 196 18.6% 33 16.8%
Primary Orbits 23,096 *2,578 11.2% 382 14.8%
*2,578 Approved does not include 16 Calibration orbits (9 Prime + 7 Internals)
3
in the history of the telescope. About nine times more orbits were requested than were available, and six times more proposals were submitted than approved. Hubble is a joint NASA–European Space Agency (ESA) mission. ESA scientists were principal investigators (PIs) on 33 of the 196 accepted proposals, accounting for 14.8% of the orbits allocated and 16.8% of the proposals.
For Cycle 18, the TAC and the panels recommended 59% of the GO prime orbits— excluding orbits of parallel observations—for spectroscopy and 41% for imaging. WFC3 is the most widely used instrument in prime mode, with a usage of 42%, followed by STIS 26%, COS 23%, ACS 9%, and FGS <1%. If parallel orbits are included in the count, the statistics are WFC3 42%, ACS 24%, STIS 18%, COS 16%, and FGS <0.1%.
The TAC and panels recommended using less than 1.5% of the available orbits for observations by NICMOS. This indicates that NICMOS still provides unique scientific capabilities on Hubble; however, those programs represent a small contribution to the overall science program. Given these circumstances, and because the restart of the NICMOS cooling system requires resources—including a significant number of orbits—the Hubble project, the Institute, and NASA Headquarters agreed that NICMOS would not be available for science in Cycle 18. Consequently, no new NICMOS observations were approved.
Configuration Mode Prime % Coordinated Parallel % Total Instrument
Prime Usage
Instrument Prime + Coordinated Parallel Usage
Pure Parallel Usage
Snap Usage
ACS/SBC Imaging 3.0% 0.0% 2.4% 0.0% 0.0%
ACS/WFC Imaging 5.7% 46.6% 13.9% 21.1% 26.7%
ACS/WFC Ramp Filter 0.2% 0.0% 0.2% 8.9% 24.2% 0.0% 0.0%
ACS/WFC Spectroscopy 0.0% 38.4% 7.7% 0.0% 0.0%
COS/FUV Spectroscopy 20.8% 0.0% 16.6% 0.0% 29.4%
COS/NUV Imaging 0.0% 0.0% 0.0% 23.1% 18.4% 0.0% 0.0%
COS/NUV Spectroscopy 2.3% 0.0% 1.8% 0.0% 0.0%
FGS POS 0.2% 0.0% 0.2% 0.2% 0.2% 0.0% 0.0%
FGS TRANS 0.0% 0.0% 0.0% 0.0% 0.0%
NIC1 Imaging 0.0% 0.0% 0.0% 0.0% 0.0%
NIC2 Imaging 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0%
NIC3 Imaging 0.0% 0.0% 0.0% 0.0% 0.0%
NIC3 Spectroscopy 0.0% 0.0% 0.0% 0.0% 0.0%
STIS/CCD Imaging 4.7% 0.0% 3.7% 0.0% 0.0%
STIS/CCD Spectroscopy 5.5% 0.0% 4.4% 0.0% 0.0%
STIS/FUV Imaging 0.2% 0.0% 0.2% 26.2% 20.9% 0.0% 0.0%
STIS/FUV Spectroscopy 10.1% 0.0% 8.1% 0.0% 19.4%
STIS/NUV Imaging 0.3% 0.0% 0.2% 0.0% 0.0%
STIS/NUV Spectroscopy 5.4% 0.0% 4.3% 0.0% 0.0%
WFC3/IR Imaging 6.8% 0.0% 5.5% 50.0% 14.8%
WFC3/IR Spectroscopy 19.9% 0.0% 15.9% 41.7% 36.3% 28.9% 0.0%
WFC3/UVIS Imaging 14.9% 15.0% 15.0% 0.0% 9.7%
WFC3/UVIS Spectroscopy 0.0% 0.0% 0.0% 0.0% 0.0%
Imaging Spectroscopy FGS
Approved GO Prime 41.0% 58.8% 0.2%
Total GO Usage ACS COS FGS NICMOS STIS WFC3
23.8% 16.0% <0.1% 0.0% 18.1% 41.9%
Instrument Statistics
Continuedpage 4
4
Proposals Accepted RatioOversubscription by Cycle
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
9.00
10.00
1 2 3 4 5 6 7 7N 8 9 10 11 12 13 14 15 16 17 18
Ove
rsub
scrip
tion
Rat
io
Cycle
GO Proposal oversubscription GO Orbit oversubscription AR Funding oversubscription
Oversubscription Ratio
CYCLE 7AR EXTENSION
Hubble Cycle 18from page 3
AGN/Quasars 5%
Cosmology 32%
ISM in External Galaxies
4% Quasar
Absorptions Lines and IGM
11%
Unresolved Stellar
9%
Cool Stars 9%
Hot Stars 4%
ISM and
Circumstellar Matter
6%
Resolved Stellar Populations
6%
Star Formation 2%
Solar System 3%
Extra-Solar
Planets 9%
Approved Orbits by Science Category
8%
Submitted Orbits by Science Category
Populations and Galaxy Structures
AGN/Quasars 11%
ISM in External Galaxies
Quasar Absorptions
Lines and IGM
Unresolved Stellar
Cool Stars
Hot Stars
ISM and
Circumstellar Matter
Resolved Stellar
Populations 9%
Star Formation 3%
Solar System 1%
Extra-Solar
Planets 7%
Populations and Galaxy Structures
Cosmology 21%
7% 18%
5%
5% 5%
5
Science ProgramThe TAC and the panels recommended a broad range
of science categories, from nearby, solar-system objects to galaxies at redshifts of z ~ 8, and utilizing the power of all Hubble instruments.
One TAC-approved program aims to collect STIS ultraviolet echelle spectra for a diverse sample of cool stars, to build an advanced spectral library for astrophysical exploration. This library will allow the detection of rare species in sharp-lined F stars, properties and kinematics of local interstellar clouds, and the dynamics of chromospheres, coronae, and winds of cool stars. Rapid public release of the data will enable many other investigations by a much wider community, no doubt continuing for decades to come.
An approved Hubble exoplanet program is scientifically complementary to Spitzer, Kepler, and COROT (Convection, ROtation and planetary Transits) results. The PI and CoIs will obtain transmission spectroscopy of the 1.4-micron water band in a sample of 13 planets, using the G141 grism of WFC3. Among the abundant molecules, only water absorbs at this wavelength, and a measurement of water abundance will remove ambiguities in the Spitzer results.
IGM science is represented by new COS G130M and G160M observations of quasi-stellar objects, which will probe the gaseous halos of dwarf galaxies well inside their virial radii. Using sensitive absorption-line measurements, the program will map the halos of low-luminosity galaxies over impact parameter to distances of 15−150 kpc. These observations will directly constrain the content and kinematics of accreting and outflowing material and will be highly relevant to the study of galaxies at high z, where shallow halos are the norm.
A 250-orbit program will provide rest-frame optical spectra for a complete sample of 9,000 galaxies at redshifts 1 < z < 3.5. It was during this period that most star formation took place, the number density of quasars peaked, the first galaxies stopped forming stars, and the structural regularity that we see in galaxies today must have emerged. The survey area will cover a subset of the fields included in the CANDELS Multi-Cycle Treasury program, amplifying the scientific returns from that program.
One pure-parallel program will use WFC3’s unique power for slitless spectroscopy to measure cosmic star formation across its peak epoch. Grism spectroscopy in deep and shallow fields will detect a sample of 2,000–3,000 emission-line galaxies in the unexplored redshift region around z = 2–3 and search Ly-α emitters at z > 5.5. A second pure-parallel program aims to search for Lyman-break galaxies at z ≈ 6−8. As the survey fields are random and completely uncorrelated, the number counts will be little affected by biases caused by statistical fluctuations. Hence, we will be able to obtain the best constraint yet on the bright-end of the luminosity function in that redshift range.
Two Legacy AR programs were recommended: one will perform a complete and consistent recalibration of all raw NICMOS polarimetric, science-imaging data in the MAST archive. The goal is to enable science deferred or previously unachieved. This program will create high-level, analysis-quality data sets with quantitative error estimates, which will be entered into the MAST for public dissemination. The second AR program will create a comprehensive, uniformly processed, well documented, and searchable collection of solar-system data obtained with WFPC2. The “planet pipeline” will populate the image headers with information unique to planetary data, and produce a science-ready collection of data.
AcknowledgmentsNumerous Institute and JHU personnel contributed to the Cycle 18 review process, both up front and
behind the scenes. Within the Science Mission Office, Daniel Apai, Neill Reid, Rachel Somerville, and Bob Williams were responsible for selecting the panelists, assigning the proposals to panels and panelists, and providing roving oversight during the review. Brett Blacker received, organized, and distributed the proposals, oversaw the proposal database, distributed the results, and prepared the statistical summaries and figures
Country Submitted Approved
Australia 11 0
Belgium 4 1Canada 15 5
Chile 7 0China 1 0Czech
Republic1 0
Denmark 6 1Finland 1 0France 16 1
Germany 38 5Greece 1 0India 2 0
Ireland 2 0Israel 5 2Italy 28 3
Japan 5 2Korea 4 1
Mexico 2 0Netherlands 11 2
Poland 2 0Portugal 2 0Russia 2 0
South Africa 6 1Spain 11 0
Sweden 6 1Switzerland 6 1
Taiwan 2 0UK 65 16
USA 788 154
ESA Proposals 198 33
Proposals by Country
Continuedpage 6
presented here. Craig Hollinshead, John Kaylor, Greg Masci, and other members of the Information Technology Services Division were responsible for developing and implementing the web-based review system. The Instruments Division and the Hubble Mission Office were responsible for technical support, and almost 30 Institute postdocs and staff provided panel support: Elizabeth Barker, Luigi Bedin, Andrea Bellini, Tiffany Borders, Azalee Bostroem, Christine Chen, Susana Deustua, Lisa Frattare, Parviz Ghavamian, David Golimowski, Aaron Grocholski, Bethan James, Pey-Lian Lim, Kevin Lindsay, Knox Long, Jack MacConnell, Ed Nelan, Sami-Matias Niemi, Cristina Oliveira, Abhijith Rajan, Michael Regan, Tony Roman, Kailash Sahu, Tony Sohn, Galina Soutchkova, Chris Thom, Tatjana Tomovic, Michael Wolfe, and Brian York. Logistical support was a particular challenge this year because of the record number of panelists. Darlene Spencer provided the overall supervision, assisted by: Karen Petro, Ronda Washington, Karyn Keidel, Roz Baxter, Tracy Bennett, Rolanda Taylor, Flory Hill, Samantha Pryce, Laura Bucklew, Ana-Maria Valenzuela, Dixie Shipley, Cheryl Schmidt, Ran Freeman, Tania Laguerre, Robin Auer, Ciera Hall, and Loretta Willers.
Assistance on the JHU side was provided by Brian Schriver, Pam Carmen, and Norma Berry, while Greg Pabst, Jeff Nesbitt, Mike Venturella, Frankie Schultz, Alford Kizer, Bill Franz, Yvette Taft, Mike Sharp, Grover Williams, Rob Levine, Phyllis Smith, James Walston, and Chad Smith (copy center) supplied Institute facilities support. Val Schnader, Ray Beaser, Paula Sessa, Karen Debelius, Margie Cook, Joe Hann, Vickie Bowersox, Lisa Kleinwort, Terry McCormack, and Dorothy Brown in the Business Resources Center, as well as John Eisenhamer and Pam Jeffries (Office of Public Outreach) were also involved in the process. Catering was provided by Irena Stein and her staff of Café Azafran.
6
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Next
Gen
erat
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of N
umer
ical
Mod
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gers
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nstra
inin
g th
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ar-f
orm
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w
Adam
Bol
ton
Univ
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ty o
f Uta
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ACS
for t
he M
asse
s: E
xten
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Stro
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ensi
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Low
er M
asse
s an
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alle
r Rad
ii
Gora
n O
stlin
Stoc
khol
m U
nive
rsity
GOLA
RS—
The
Lym
an-a
lpha
Ref
eren
ce S
ampl
e
Toru
Mis
awa
Shin
shu
Univ
ersi
tyGO
Thre
e-di
men
sion
al M
appi
ng o
f the
Mag
ella
nic
Brid
ge b
y Hi
gh-r
esol
utio
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ectro
scop
y to
war
d M
ultip
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ight
lines
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Tele
scop
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ienc
e In
stitu
teGO
Feed
back
bet
wee
n St
ars,
ISM
and
IGM
in IR
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inou
s Ga
laxi
es
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7
Luis
Ho
Carn
egie
Inst
itutio
n of
Was
hing
ton
ARA
Com
preh
ensi
ve R
e-ev
alua
tion
of th
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latio
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twee
n Bl
ack
Hole
M
ass
and
Bulg
e Lu
min
osity
in N
earb
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tive
Gala
xies
Aaro
n Ba
rth
Univ
ersi
ty o
f Cal
iforn
ia -
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neGO
A De
finiti
ve G
as-d
ynam
ical
Mea
sure
men
t of t
he B
lack
Hol
e M
ass
in M
87
Luis
Ho
Carn
egie
Inst
itutio
n of
Was
hing
ton
GOA
New
Sam
ple
of C
ircum
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ear G
as D
isks
for M
easu
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Blac
k Ho
le M
asse
s in
Spi
ral G
alax
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Sim
on M
orris
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ersi
ty o
f Dur
ham
GOTh
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latio
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p be
twee
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s an
d Ga
laxi
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r 0 <
z <
1.2
Scot
t And
erso
nUn
iver
sity
of W
ashi
ngto
nGO
Span
ning
the
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niza
tion
Hist
ory
of IG
M H
eliu
m: A
Hig
hly
Effic
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Spe
ctra
l Sur
vey
of th
e Fa
r-UV
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htes
t Qua
sars
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taer
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iver
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alifo
rnia
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erke
ley
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Mod
els
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isru
ptio
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Sta
rs b
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assi
ve B
lack
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lesc
ope
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nce
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itute
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pect
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t-re
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ft Bl
ack
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Can
dida
tes
Eric
Hal
lman
Harv
ard
Univ
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tyAR
Unde
rsta
ndin
g th
e IG
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bsor
bers
with
Num
eric
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imul
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f the
WHI
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hns
Hopk
ins
Univ
ersi
tyGO
Reio
niza
tion
of In
terg
alac
tic H
eliu
m a
t the
Hig
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Red
shift
s
Mic
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nnsy
lvan
ia S
tate
Uni
vers
ityGO
Spec
trosc
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Sig
natu
res
of B
inar
y an
d Re
coilin
g Bl
ack
Hole
s
J. C
hris
toph
er H
owk
Univ
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f Not
re D
ame
SNAP
A CO
S Sn
apsh
ot S
urve
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r z <
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5 Ly
man
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it Sy
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s
Gary
Fer
land
Univ
ersi
ty o
f Ken
tuck
yAR
Plas
ma
Sim
ulat
ions
that
Mee
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Cha
lleng
es o
f CO
S an
d ST
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D. M
icha
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rens
haw
Geor
gia
Stat
e Un
iver
sity
Re
sear
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ound
atio
nGO
Wha
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tions
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emat
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of M
ass
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AG
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onUn
iver
sity
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Low
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shift
Dam
ped
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an-a
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Sys
tem
s Se
lect
ed b
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cm
Abs
orpt
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A N
ew R
oute
to H
igh
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Robe
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lard
Spa
ce S
cien
ce L
abor
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Map
ping
the
Core
and
Lob
es o
f the
Ext
raor
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RII M
icro
quas
ar in
NGC
779
3
Xiao
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anUn
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sity
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aSN
APA
SNAP
Sur
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for G
ravi
tatio
nal L
ense
s am
ong
z ~
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rs
Jenn
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eene
Prin
ceto
n Un
iver
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GOTh
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sts
of M
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k Ga
laxi
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Dani
el P
roga
Univ
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f Nev
ada
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gas
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Emis
sion
and
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Line
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ontri
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m D
isk
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ley
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ate
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Fou
ndat
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ccur
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Blac
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ass
Estim
ates
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John
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ace
Tele
scop
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ienc
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stitu
teGO
High
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cisi
on P
rope
r Mot
ions
in th
e M
87 J
et
Sean
Far
rell
Univ
ersi
ty o
f Lei
cest
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The
Ultra
viol
et a
nd O
ptic
al C
ount
erpa
rts
of th
e In
term
edia
te-m
ass
Blac
k Ho
le C
andi
date
ESO
243
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HLX-
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Jess
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nber
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orge
Mas
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nive
rsity
GOUn
rave
lling
the
Mys
terie
s of
the
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Ring
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rptio
n-lin
e St
udy
of a
n Un
usua
l Gas
Clo
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Bart
Wak
ker
Univ
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ty o
f Wis
cons
in -
Mad
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GOM
appi
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Nea
rby
Gala
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ilam
ent
Herm
an M
arsh
all
Mas
sach
uset
ts In
stitu
te o
f Tec
hnol
ogy
GORe
solv
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the
Pict
or A
Jet
Chris
toph
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hurc
hill
New
Mex
ico
Stat
e Un
iver
sity
GOTh
e Re
lativ
e Ki
nem
atic
s of
Gal
axy
Emis
sion
and
Mul
tiple
Gas
Pha
ses
in z
~ 0
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xten
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xy H
alos
Eric
Mon
ier
Stat
e Un
iver
sity
of N
ew Y
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t Bro
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Cosm
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etal
licity
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orpt
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line
Syst
ems
near
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shift
z =
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hlin
sky
Scie
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and
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, Inc
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Usin
g HS
T/W
FC3
to C
onst
rain
the
Lym
an C
utof
f an
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lors
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nfra
red
Back
grou
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luct
uatio
ns
Dete
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amun
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guri
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stro
nom
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Unde
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t Qua
sar L
ens
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J10
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Chun
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i Ma
Univ
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ty o
f Cal
iforn
ia -
Ber
kele
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Mer
gers
of D
ark
Mat
ter H
alos
and
Gal
axie
s in
a L
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Uni
vers
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Willi
am S
park
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ace
Tele
scop
e Sc
ienc
e In
stitu
teGO
Prob
ing
the
Phys
ics
of G
as in
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l-cor
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rs: V
irgo
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arch
esin
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fts U
nive
rsity
ARCo
nstra
inin
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ass
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ella
r Mas
s Fu
nctio
n at
z =
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Cycle 18: Approved Observing ProgramsNa
me
Inst
itutio
nTy
peTi
tle
8
Fred
eric
Cou
rbin
Ecol
e Po
lyte
chni
que
Fédé
rale
de
Laus
anne
GOSt
rong
Gra
vita
tiona
l Len
sing
by
Qua
sars
Greg
ory
Rudn
ick
Univ
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ty o
f Kan
sas
Cent
er
for R
esea
rch,
Inc.
ARSe
para
ting
Envi
ronm
enta
l Trig
gers
of M
orph
olog
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Tra
nsfo
rmat
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and
Star
-for
mat
ion
Que
nchi
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Nial
Tan
vir
Univ
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ty o
f Lei
cest
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Iden
tifyi
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nd S
tudy
ing
Gam
ma-
ray
Burs
ts a
t Ver
y Hi
gh R
edsh
ifts
Rode
rick
John
ston
eUn
iver
sity
of C
ambr
idge
GOPr
obin
g In
term
edia
te Io
niza
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Gas
in th
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rseu
s an
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Clus
ters
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las
Clow
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Univ
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ity in
the
Cros
sfire
: Rev
ealin
g th
e Pr
oper
ties
of D
ark
Mat
ter i
n Bu
llet-
like
Clus
ters
Priy
amva
da N
atar
ajan
Yale
Uni
vers
ityAR
Prob
ing
the
Rela
tion
betw
eeen
Lig
ht a
nd M
ass
Com
bini
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lexi
on w
ith S
hear
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ngko
ok J
eeUn
iver
sity
of C
alifo
rnia
- D
avis
ARPr
inci
pal C
ompo
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lysi
s of
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for W
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and
ACS/
WFC
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egre
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pen
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tyGO
High
-res
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Near
-infra
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Imag
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of t
he F
irst
Sub-
mm
Sel
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d Gr
avita
tiona
l Len
s Ca
ndid
ates
in t
he H
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hel
Astro
phys
ical
Ter
aher
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arge
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a Su
rvey
(H-A
TLAS
)
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ld E
belin
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of H
awai
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APA
Snap
shot
Sur
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of th
e M
ost M
assi
ve C
lust
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of G
alax
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Rupa
l Mitt
alRo
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ter I
nstit
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of T
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Link
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For
mat
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with
Intra
clus
ter M
ediu
m C
oolin
g an
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N He
atin
g in
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ampl
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chel
Gal
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ters
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belin
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of H
awai
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An In
-dep
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of D
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ter i
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r MAC
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Eric
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Labo
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Gala
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ias
Mea
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men
t with
Wea
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nsin
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CO
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Rom
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avé
Univ
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f Ariz
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diat
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Hydr
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Sim
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of R
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xies
Wal
ter J
affe
Ster
rew
acht
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den
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Sta
rs Io
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the
Fila
men
ts in
NGC
127
5?
Tom
mas
o Tr
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iver
sity
of C
alifo
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a Ba
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SWEL
LS: D
oubl
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the
Num
ber o
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k-do
min
ated
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Spi
ral L
ens
Gala
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Davi
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dbur
n-Sm
ithUn
iver
sity
of W
ashi
ngto
nGO
Disk
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ncat
ions
: Pro
bing
Gal
axy
Form
atio
n at
the
Lim
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Rich
ard
Ellis
Calif
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stitu
te o
f Tec
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GOTo
war
ds a
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sica
l Und
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f Typ
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vae
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Res
earc
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unda
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ARA
Deta
iled
Anal
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of S
tella
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in G
alax
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Durin
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Kent
aro
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min
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of N
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Las
Vega
sAR
Phys
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pert
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of H
igh-
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hift
WFC
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laxi
es a
t z =
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0
Ole
g Gn
edin
Univ
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ty o
f Mic
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Mod
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Lum
inos
ity o
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ft Ga
laxi
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Chris
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rvar
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GOW
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Lens
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Mas
s Ca
libra
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of S
Z-se
lect
ed C
lust
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Gala
ctic
Pro
gram
sAt
a Sa
raje
dini
Univ
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ty o
f Flo
rida
ARVa
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e St
ars
in th
e An
drom
eda
Syst
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Leo
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Oss
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GOTh
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of M
ultip
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ain-
sequ
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Tur
n-of
fs a
nd D
ual R
ed C
lum
ps in
Mag
ella
nic
Clou
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ar C
lust
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Paul
a Sz
kody
Univ
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ty o
f Was
hing
ton
GOAn
Unp
rece
dent
ed O
ppor
tuni
ty to
Fol
low
Fou
r Acc
retin
g W
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to th
e In
stab
ilty
Strip
Doug
las
Gies
Geor
gia
Stat
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iver
sity
Re
sear
ch F
ound
atio
nGO
Hot E
volv
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ompa
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s to
Inte
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-mas
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sequ
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Sta
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Scot
t Frie
dman
Spac
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lesc
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Scie
nce
Inst
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odel
s of
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teriu
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eple
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volu
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Impr
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men
ts o
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for t
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nito
r of t
he T
ype
Ib S
uper
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ocho
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Inst
itute
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libra
ting
the
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Lum
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f Red
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mp
Star
s: A
n Ar
chiv
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tudy
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tar C
lust
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nive
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GOGl
obul
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lust
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alax
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ildin
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ocks
Tuan
Do
Univ
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ty o
f Cal
iforn
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Los
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GOM
easu
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the
Phys
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Pro
pert
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of th
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ilky
Way
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Sta
r Clu
ster
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per M
otio
ns
Giam
paol
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otto
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ultip
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tella
r Pop
ulat
ions
in G
alac
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lobu
lar C
lust
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Cycle 18: Approved Observing ProgramsNa
me
Inst
itutio
nTy
peTi
tle
9
Stev
en F
eder
man
Univ
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ty o
f Tol
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ARCo
ntrib
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sive
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rs to
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Willi
am H
arris
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aste
r Uni
vers
ityGO
Supe
rmas
sive
Sta
r Clu
ster
s in
Sup
ergi
ant G
alax
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Tra
cing
the
Enric
hmen
t of t
he E
arlie
st S
tella
r Sys
tem
s
Just
yn M
aund
Univ
ersi
ty o
f Cop
enha
gen,
Ni
els
Bohr
Inst
itute
GOSt
ella
r For
ensi
cs II
: A P
ost-
expl
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n Vi
ew o
f the
Pro
geni
tors
of C
ore-
colla
pse
Supe
rnov
ae
Andr
ew L
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The
Univ
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ty o
f War
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otio
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pern
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ich
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f Cal
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t Ste
llar C
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orph
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iver
sità
di P
adov
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Mul
tiple
Ste
llar G
ener
atio
ns in
the
Larg
e M
agel
lani
c Cl
oud
Star
Clu
ster
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184
6
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uim
byCa
lifor
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of T
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g th
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ight
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eath
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ical
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Nam
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13
14
Name Institution Panel
TAC Members
Neta Bahcall Princeton University TAC Chair
Michael Eracleous The Pennsylvania State University TAC At Large Member
John Huchra Harvard University TAC At Large Member
Jim Pringle University of Cambridge TAC At Large Member
Extra Galactic Panel Members
Roberto Abraham University of Toronto Exgal Panel Chair
Lee Armus California Institute of Technology Extra Galactic
Daniel Batcheldor Florida Institute of Technology Extra Galactic
Eric Bell University of Michigan Exgal Panel Chair
Misty Bentz University of California - Irvine Extra Galactic
Michael Blanton New York University Extra Galactic
Marusa Bradac University of California - Davis Extra Galactic
Jean Brodie University of California - Santa Cruz Extra Galactic
Jane Charlton The Pennsylvania State University Exgal Panel Chair
Christopher Churchill New Mexico State University Extra Galactic
Emanuele Daddi CEA/DSM/DAPNIA/Service d'Astrophysique Extra Galactic
Charles Danforth University of Colorado at Boulder Extra Galactic
Gabriella De Lucia INAF, Osservatorio Astronomico di Trieste Extra Galactic
Duilia de Mello NASA Goddard Space Flight Center Extra Galactic
Tiziana Di Matteo Carnegie Mellon University Extra Galactic
Megan Donahue Michigan State University Exgal Panel Chair
Reginald Dufour Rice University Extra Galactic
Derek Fox The Pennsylvania State University Extra Galactic
Johan Fynbo University of Copenhagen, Niels Bohr Institute Extra Galactic
Martin Gaskell University of Texas at Austin Extra Galactic
Mark Giroux East Tennessee State University Extra Galactic
Genevieve Graves University of California - Berkeley Extra Galactic
Jenny Greene Princeton University Extra Galactic
Raja Guhathakurta University of California - Santa Cruz Extra Galactic
Knud Jahnke Max-Planck-Institut für Astronomie, Heidelberg Extra Galactic
Lisa Kewley University of Hawaii Extra Galactic
Juna Kollmeier Carnegie Institution of Washington Extra Galactic
Chryssa Kouveliotou NASA Marshall Space Flight Center Extra Galactic
Mariska Kriek Princeton University Extra Galactic
Ivo Labbe Carnegie Institution of Washington Extra Galactic
Tod Lauer National Optical Astronomy Observatories Extra Galactic
Karen Leighly University of Oklahoma Norman Campus Extra Galactic
Jennifer Lotz National Optical Astronomy Observatories Extra Galactic
Lauren MacArthur Dominion Astrophysical Observatory Extra Galactic
Sangeeta Malhotra Arizona State University Extra Galactic
Paul Martini The Ohio State University Research Foundation Extra Galactic
Karin Menendez-Delmestre Carnegie Institution of Washington Extra Galactic
Leonidas Moustakas Jet Propulsion Laboratory Extra Galactic
Priyamvada Natarajan Yale University Extra Galactic
Cycle 18: TAC and Panel Members
Roderik Overzier Max-Planck-Institut für Astrophysik Extra Galactic
Michael Pahre Smithsonian Institution Astrophysical Observatory Extra Galactic
Chien Peng Dominion Astrophysical Observatory Extra Galactic
Eric Peng Peking University Extra Galactic
Laura Pentericci INAF, Osservatorio Astronomico di Roma Extra Galactic
Maria Polletta Istituto Nazionale di Astrofisica Extra Galactic
Cristina Popescu University of Central Lancashire Extra Galactic
Moire Prescott University of California - Santa Barbara Extra Galactic
Marina Rejkuba European Southern Observatory - Germany Extra Galactic
Jane Rigby Carnegie Institution of Washington Extra Galactic
Sara Salimbeni University of Massachusetts Extra Galactic
Dave Sanders University of Hawaii Exgal Panel Chair
Claudia Scarlata California Institute of Technology Extra Galactic
Daniel Schaerer Observatoire de Genève Extra Galactic
Ricardo Schiavon Gemini Observatory, Northern Operations Extra Galactic
Jennifer Scott Towson University Extra Galactic
Nick Scoville California Institute of Technology Extra Galactic
Alice Shapley University of California - Los Angeles Exgal Panel Chair
Alicia Soderberg Harvard University Extra Galactic
Geneviève Soucail Observatoire Midi-Pyrénées Extra Galactic
John Stocke University of Colorado at Boulder Extra Galactic
Tommaso Treu University of California - Santa Barbara Extra Galactic
Todd Tripp University of Massachusetts Extra Galactic
Marianne Vestergaard University of Copenhagen, Niels Bohr Institute Extra Galactic
Nicole Vogt New Mexico State University Extra Galactic
David Weinberg The Ohio State University Research Foundation Extra Galactic
Ben Weiner University of Arizona Extra Galactic
Liliya Williams University of Minnesota - Twin Cities Extra Galactic
Rogier Windhorst Arizona State University Exgal Panel Chair
Guy Worthey Washington State University Extra Galactic
Sukyoung Yi Yonsei University Extra Galactic
Nadia Zakamska Institute for Advanced Study Extra Galactic
Galactic Panel Members
Thomas Ayres University of Colorado at Boulder Galactic
Francesca Bacciotti Osservatorio Astrofisico di Arcetri Galactic
Isabelle Baraffe University of Exeter Galactic
Beatriz Barbuy Universidade de São Paulo Galactic
Arjan Bik Max-Planck-Institut für Astronomie, Heidelberg Galactic
Robert Blum National Optical Astronomy Observatories Galactic
Fabio Bresolin University of Hawaii Galactic
Cesar Briceño Centro de Investigaciones de Astronomía Galactic
Sean Brittain Clemson University Galactic
Adam Burgasser University of California - San Diego Galactic Panel Chair
Paul Crowther University of Sheffield Galactic Panel Chair
Andrew Dolphin Raytheon Company Galactic
Name Institution Panel
Cycle 18: TAC and Panel Members
15
Gaspard Duchene University of California - Berkeley Galactic
Andrea Dupree Smithsonian Institution Astrophysical Observatory Galactic
Annette Ferguson Royal Observatory Edinburgh Galactic
Peter Garnavich University of Notre Dame Galactic
Marla Geha Yale University Galactic
William Harris McMaster University Galactic
Suzanne Hawley University of Washington Galactic Panel Chair
Sara Heap NASA Goddard Space Flight Center Galactic
Alexander Heger University of Minnesota - Twin Cities Galactic
Ulrike Heiter Uppsala Astronomical Observatory Galactic
Gregory Herczeg Max-Planck-Institut für extraterrestrische Physik Galactic
Jon Holtzman New Mexico State University Galactic
Joseph Hora Smithsonian Institution Astrophysical Observatory Galactic
Ivan Hubeny University of Arizona Galactic
Edward Jenkins Princeton University Galactic Panel Chair
Saurabh Jha Rutgers the State University of New Jersey Galactic
Kelsey Johnson The University of Virginia Galactic
Lex Kaper Universiteit van Amsterdam Galactic
Christian Knigge University of Southampton Galactic
John Lattanzio Monash University Galactic
Jeffrey Linsky University of Colorado at Boulder Galactic
Kevin Luhman The Pennsylvania State University Galactic
Massimo Marengo Iowa State University Galactic
Stephan McCandliss The Johns Hopkins University Galactic
Maryam Modjaz University of California - Berkeley Galactic
Patrick Morris California Institute of Technology Galactic
Bob O'Dell Vanderbilt University Galactic
Anne Pellerin Texas A&M Research Foundation Galactic
Klaus Pontoppidan California Institute of Technology Galactic
Michael Rich University of California - Los Angeles Galactic
Harvey Richer University of British Columbia Galactic
Abhijit Saha National Optical Astronomy Observatory Galactic
Richard Shaw National Optical Astronomy Observatory Galactic
Edward Sion Villanova University Galactic
Verne Smith National Optical Astronomy Observatories Galactic
Nicholas Sterling Michigan State University Galactic
Susan Terebey California State University - Los Angeles Galactic
Saeqa Vrtilek Smithsonian Institution Astrophysical Observatory Galactic
Lifan Wang Texas A&M Research Foundation Galactic
Dennis Zaritsky University of Arizona Galactic Panel Chair
Planetary Panel Members
David Ardila California Institute of Technology Planetary
Marc Buie Southwest Research Institute Planetary
John Debes NASA Goddard Space Flight Center Planetary
Name Institution Panel
Cycle 18: TAC and Panel Members
16
Drake Deming NASA Goddard Space Flight Center Planetary
Paul Feldman The Johns Hopkins University Planetary Panel Chair
Alan Fitzsimmons Queen's University Planetary
Erika Gibb University of Missouri - St. Louis Planetary
James Graham University of California - Berkeley Planetary Panel Chair
Caitlin Griffith University of Arizona Planetary
Amanda Hendrix Jet Propulsion Laboratory Planetary
Michael Jura University of California - Los Angeles Planetary
William Merline Southwest Research Institute Planetary
Glenn Orton Jet Propulsion Laboratory Planetary
Marshall Perrin University of California - Los Angeles Planetary
Aki Roberge NASA Goddard Space Flight Center Planetary
Scott Sheppard Carnegie Institution of Washington Planetary
David Sing University of Exeter Planetary
Mark Swain Jet Propulsion Laboratory Planetary
Anne Verbiscer The University of Virginia Planetary
Name Institution Panel
Cycle 18: TAC and Panel Members
17
The Hubble Multi-Cycle Treasury Science ProgramI. Neill Reid, [email protected], and Suzanne L. Hawley, [email protected]
SummaryServicing Mission 4 (SM4) had the prime goal of maximizing the scientific productivity of the Hubble
Space Telescope for the subsequent five years. Following SM4’s successful completion, Hubble has its most powerful suite of instrumentation. The Call for Multi-Cycle Treasury (MCT) Programs issued in 2009 was designed to provide the community with an opportunity to exploit those enhanced capabilities, and to help achieve the overarching goal of SM4. The MCT Time Allocation Committee (TAC) met early this year, and recommended execution of three observing programs that incorporated science from four MCT proposals. The observing time for those programs, which includes contributions from both the general observer (GO) pool and Director’s Discretionary (DD) time, will be distributed over at least three cycles, starting in Cycle 18.
IntroductionHubble was launched in April 1990. During the succeeding 20 years, it has revolutionized our
understanding in diverse fields, including: galaxy formation and evolution; the properties of active nuclei and the development of black holes; the structure and evolution of the intergalactic and interstellar media; stellar populations in different environments; Galactic and extragalactic star formation; the characteristics of circumstellar disks and exoplanet atmospheres; and the detailed properties of denizens of our own Solar System. This scientific diversity and impact reflect, at least in part, the way that Hubble time is allocated—with observing programs that range in scope from small, narrowly focused investigations of individual targets, to extensive survey programs that enable progress on multiple research topics.
From the outset of the Hubble program, there was clear recognition that different scientific questions demand a range of resources, and that Hubble would only reach its full potential if that concept was realized in the time-allocation process. Thus, in 1986 the Space Telescope Advisory Council recommended that time be divided equally among small, medium and large programs, where “large” programs were defined as those requiring more than 100 orbits. This directive was repeated in the first (and succeeding) Call for Proposals, but to little avail. As the Hubble Second Decade Committee (2DC) commented, in Cycles 1 to 8 only 18 of 2,173 GO programs received allocations of more than 50 orbits, and only 5 more than 100 orbits.
Formally, the Institute Director allocates time on Hubble, but generally does so based on recommendations made by the TAC. In these early cycles, all GO (and SNAP) proposals were graded and ranked by specialist panels, with the TAC merging proposals from the various disciplines. Selection
committees have an inherent desire to try to please as many applicants as possible. Faced with a limited budget, there is a tendency to favor smaller proposals, as each panel is reluctant to allocate a significant fraction of its resources to a single proposal. Indeed, one can show statistically that the breakpoint comes where a proposal requires more than 20% of the orbits available to a panel.
The 2DC recognized this issue, and recommended that 20–30% of Hubble’s orbits be set aside specifically for larger-scale Treasury Programs. Other 2DC recommendations included establishing a committee that would both actively solicit Treasury proposals from the community, and work with successful PIs to refine their science programs. The resultant report was instrumental in leading to the current TAC structure, first implemented in Cycle 11. Broad-based panels allocate approximately two-thirds of the available orbits (2,100 to 2,220 orbits in a typical cycle) to small and medium-sized programs that require less than 100 orbits, with the remainder of the time (~1,100 orbits) reserved for the TAC to allocate to Large and Treasury programs. Treasury Programs are defined as large-scale proposals that address complex, high-impact scientific issues, providing enhanced datasets that are of lasting value to the broader astronomical community.
Since Cycle 11, the Hubble TAC has recommended acceptance of 13 Treasury Programs and 56 Large Programs for a total of 7,686 prime and 3,779 parallel orbits. The overall distribution (Figure 1) shows that
18
Orbits
Num
ber
Hubble Large/Treasury Programs
Figure 1: Size distribution of Hubble Large and Treasury programs
Continuedpage 20
19
the TAC follows the panel in its reluctance to support very large programs. While there are some notable exceptions, including the ACS Nearby Galaxy Survey, the H0 Key Project, PANS, GOODS and COSMOS, the typical successful Large/Treasury program requests between 100 and 200 orbits (i.e., less than 20% of the TAC orbit budget), and the median allocation is ~130 orbits. These programs, which range from detailed investigations of the kinematics and chemistry of Eta Carinae and maps of the Orion Nebula, to surveys of the Coma galaxy cluster and deep imaging to probe galaxy formation and evolution in select fields, have pushed the observational frontiers and achieved results with broad scientific impact. However, it has become clear in recent cycles that an increasing number of projects require resources that extend beyond the comfort level of TAC allocations. Just as 100+ orbit programs fared poorly against small and medium programs in Cycles 1–8, 300+ orbit programs carry significant psychological overheads when considered in the current TAC process. Clearly, programs that ask for such extensive resources must also promise corresponding scientific returns, but the expense is so high that it becomes very difficult for them to receive fair consideration. The MCT Program was designed to provide an opportunity for such large programs to be judged separately, on their own merits.
Designing the MCT ProgramThe concept of MCT observing programs was initially raised with the community in mid-2007,
subsequent to the Cycle 17 TAC review. The first step was determining whether there was community support for high-impact science programs on this scale. To that end, and following consultations with the Space Telescope Users Committee (STUC), the Institute issued a call for white papers describing science projects that require allocations of at least 400 orbits. Contributors were tasked with explaining why those projects were of sufficient importance to require allocations on that scale, and to explain why those projects could not be undertaken under the current scheme. At the same time, the community was given an opportunity to weigh in against the concept, summarizing any detrimental impact envisaged on Hubble science.
A total of 22 white papers were received by the deadline of 30 November 2007. Three argued against the concept, voicing concerns that specific science areas would suffer as a consequence of implementing the process. The remaining 19 white papers were favorable, advocating science programs that the authors believed required MCT-scale allocations. The white papers were reviewed by a small ad hoc committee comprising two external scientists, Prof. Malcolm Longair (Cambridge University) and Prof. Brad Peterson (The Ohio State University, at that time Chair of the Space Telescope Institute Committee), and two internal Institute research staff, Bob Williams (former Institute Director and current President of the International Astronomical Union), and Neill Reid (Head of the Science Policies Division at that time). In order to ensure impartiality, all the committee members agreed that they would not participate in any MCT proposals, should the program go ahead.
The committee concluded that it was likely that important scientific results could be achieved through this initiative. Based on their report, the Director decided in January 2008 that the program should be implemented. Following discussions with the STUC, the following guidelines were adopted:
• MCTproposalswouldbesolicitedseparatelyfromstandardHubble proposals, and assessed by a separate TAC. No member of the MCT TAC should be involved an MCT proposal.
• Therewouldbenorestrictionorpre-selectionofsciencetopicsaspartoftheMCTcallforproposals.
• TheMCTTACwasauthorizedtorecommendrejectionofallproposalsif,intheirjudgment,none merited allocation of such a large number of Hubble orbits. Any selected programs would have zero proprietary time.
• TheselectionprocesswastobecompletedbeforethestandardCycle18PhaseIdeadline,allowing an opportunity for standard proposers to assess the likely impact of any accepted MCT proposals on their program, and permitting unsuccessful MCT proposers to recast their proposals. Some consideration was also given to allowing archival programs in Cycle 18, but, after discussion with the STUC, the decision was taken to postpone this opportunity until the Cycle 19 call.
• Upto750orbitspercyclewouldbemadeavailableforMCTobservingprogramsinCycles18 and 19, comprising up to 500 orbits of GO time and up to 250 orbits of DD time. The GO orbits were to be drawn primarily from the current allocation to Large and Treasury programs, minimizing the impact on small and medium programs.
• MCTproposers had the option of requesting timeallocations in any future cycle, as longas they provided a clear scientific justification. The MCT TAC would also have the ability to allocate time in future cycles, should they feel that it was warranted by the science.
• CallsforMCTproposalswouldnotbeissuedonanannualbasis.Indeed,dependingontheresults from the initial call and the prognosis of Hubble instrumentation, there might not be any subsequent calls.
20
Hubble Multi-cyclefrom page 19
MCT Schedule and TAC ProcessIn January 2008 when the selected MCT observing programs were announced, SM4 was still
scheduled for August 2008. The initial schedule envisioned that the Call for Proposals would be issued in mid-2008, with a mid-October Phase I deadline. As the timing of SM4 changed, with an initial slip to October 2008 and then re-phasing to mid-2009 following the failure of the Science Instrument Control and Data Handler, the MCT schedule evolved accordingly. In particular, the decision was made to delay the call until after SM4 was completed, permitting a more reliable assessment of the available instrumentation at the expense of a relatively compressed schedule for the MCT TAC process to mesh with the Cycle 18 proposal schedule.
As we all know, SM4 was an unqualified success, leaving Hubble with two new and two refurbished instruments. The Call for Proposals was issued mid-August 2009, with the Phase I deadline set for 18 November 2009. The MCT TAC was scheduled to meet in early January 2010, allowing proposers to be notified by late January, well in advance of the Cycle 18 Phase I deadline of 27 February 2010. The Institute also issued a request to the community for (non-binding) notices of intent (NOIs), with the aim of gauging the range of community interest, assessing the types of programs, and identifying scientists that would be ineligible for TAC membership. In this regard, the NOI exercise was only partially successful, since while 22 NOIs were submitted, some 39 proposals were received by the Phase I deadline. These proposals involved 785 unique participants (as PI or co-I) and requested some 26,801 orbits (see Table 1 for the breakdown by science topic). As a guide, this corresponds to a 17:1 oversubscription for the baseline 2-cycle allocation discussed in the MCT call for proposals.
As is customary, the MCT proposals were distributed for initial grading by the members of the MCT TAC. The TAC was chaired by Suzanne Hawley (U. Washington). The other TAC members were Roger Davies (Oxford), Jim Pringle (Cambridge), Ken Freeman (Australian National University), Christine Jones-Forman (Smithsonian Astrophysical Observatory), Greg Laughlin (U.C. Berkeley), Mario Mateo (U. Michigan, the current chair of the STUC) and Daniel Eisenstein (U. Arizona). Three further scientists were asked to provide supplementary information as external referees, but, in actuality, additional input was only received from Bob Williams. All TAC members and external referees were asked to grade all proposals, and preliminary grades were received by 30 December 2009. Given the oversubscription, the formal triage level was set to eliminate the 16 proposals with the lowest average grades.
The MCT TAC met in Baltimore, at the Inn at the Colonnade, on Friday January 8 and Saturday January 9, 2010. The meeting was also attended by the Institute Director, the newly-appointed Deputy Director, John Grunsfeld, and the Head of Science Mission, Neill Reid. George
Sonnenborn, the acting Hubble Project Scientist, and Mal Niedner, the Deputy Project Scientist, attended as external observers, representing the Hubble Project.
In reviewing the MCT proposals, the TAC was asked to provide feedback on key science areas for Hubble and to consider the specific aim of maximizing the science produced by Hubble over the next five years. Given this goal, the TAC had greater latitude than usual in suggesting changes to proposals, and even combining proposals, in order to ensure that the best possible science program was recommended for what might be a unique opportunity to utilize such extensive resources operating at peak efficiency.
Logistically, the TAC followed a three-step process. Grouping proposals by science area, the TAC first identified which should be discussed in detail. This step included consideration of the triaged proposals. Next, the TAC determined which proposals met the three main MCT criteria:
• Scientific merit: did the proposal offer the potential of solving a key, high-impact scientificquestion or questions?
• SuitabilityasanMCTobservingprogram:canthesciencegoalsonlybeachievedbyanMCTproposal, rather than through the standard Hubble time-allocation process?
• Legacyvalue:does theprogramproduceadataset thatwillhave lastingvalue for theastronomical community?
Finally, the TAC produced a rank-ordered list of the proposals that were judged suitable as MCT observing programs.
Some 22 of the 39 proposals were discussed in detail by the MCT TAC. Most of these proposals—and, indeed, some the proposals that were not discussed—were regarded as scientifically very interesting. Nevertheless, many failed to meet the MCT criteria. Specifically, a significant number failed to provide a strong justification for why an MCT-scale program was required to tackle the underlying scientific questions. Indeed, some undermined their case from the outset by proposing segregated programs that addressed multiple, quasi-independent goals. Consequently, only seven proposals were carried through to the final ranking.
Proposals Orbits Category
2 1015 AGN/quasars
1 540 Cool stars
11 7437 Cosmology
5 3007 Extrasolar planets
2 1090 Hot stars
1 1163 ISM & CS matter
6 4469 QSO abs. lines & ISM
5 3869 Resolved stellar populations
1 490 Solar system
5 3741 Unresolved stellar populations
Table 1: Statistics on MCT proposal submissions
21
The seven proposals to reach final ranking represent four science areas: investigations of galaxy formation and evolution through multi-tiered imaging surveys; probing dark energy through high-redshift supernovae surveys; detailed examination of the structure of galaxy clusters; and comprehensive surveys of resolved stellar populations in nearby galaxies. All four science areas were regarded by the MCT TAC as being both highly important, and in areas where Hubble could make a significant contribution in the next five years. Two further topics, exoplanet research and investigations of the intergalactic medium, were flagged as key science areas for Hubble. These conclusions, together with comments and a final ranking of the seven proposals, were presented to the Institute Director at the conclusion of the TAC meeting.
MCT ResultsThe MCT Program is an extraordinary opportunity to tackle major projects with instrumentation
working close to its peak performance. Consequently, the strategy adopted to implement the MCT TAC recommendations differed from the usual approach. In order to maximize the scientific return, the Director decided to allocate time to three observing programs that incorporate science from four MCT proposals.
1. “A Panchromatic Hubble Andromeda Survey: UV/optical/near-IR imaging of one quadrant of M31.” (PI J. Dalcanton, U. Washington) 834 orbits.
2. “Through a Lens, Darkly—New Constraints on the Fundamental Components of the Cosmos.” A multicolor (14-band) imaging survey of 25 galaxy clusters, coupled with a high-redshift supernova search in coordinated parallel observations. (PI: M. Postman, STScI) 524 orbits.
3. “A Deep Near-Infrared Survey.” WFC3 and ACS imaging of multiple fields to probe galaxy assembly, coupled with a high-redshift supernova survey. (PI: S. Faber, UCSC; co-PI: H. Ferguson, STScI) 902 orbits.
The last program combines elements of two separate MCT proposals, specifically the tiered imaging structure proposed by Faber’s team to investigate galaxy evolution, and the observing strategies developed by Ferguson’s team to search for high-redshift supernovae. In addition, there are potential synergies that need to be explored between this program and the supernova search conducted as part of the galaxy cluster survey. This outcome represents a departure from past practice, although there is precedent for TAC panels modifying individual proposals (e.g., COSMOS) and, more rarely, requiring cooperation between programs.
This set of recommendations was discussed in detail with the MCT TAC Chair, and circulated to all of the MCT TAC members on January 13. There was full concurrence. The Director also circulated his implementation plan to the AURA President, the chair of the Space Telescope Institute Council, the chair of the AURA Board, the Hubble Project at Goddard, and NASA Headquarters. The Director discussed these recommendations directly with Jon Morse, director of the Astrophysics Division. In each case, there was concurrence in the proposed allocation of observing time, explicitly including the merging of the Faber and Ferguson proposals.
Given this broad concurrence, the Director contacted the PIs of the successful proposals. PIs Faber and Ferguson agreed to start the process of merging their programs, working within a fixed orbit budget and in a manner that followed specific TAC guidelines: preserving the two-tier nature of the Faber proposal, but reducing the wide/shallow coverage; and including explicit follow-up for high-redshift supernovae. At the same time, the Faber/Ferguson team embarked on discussions with the Postman team concerning means of combining and optimizing the supernova follow-up programs.
On 18 January 2010, all PIs and co-Is of MCT proposals were informed by e-mail of the TAC results with regard to their proposals. The results were publicized to the broader community via the Cycle 18 AO web pages, and through individual web pages for each program. It is important to recognize that the detailed information available for typical Hubble observing programs is drawn from Phase ΙΙ proposals. Each MCT program is extremely complex, and there was no possibility of developing information at that level before the Cycle 18 deadline—indeed, while the Phase ΙΙ deadlines were set for April 23, scheduling information will not be available until the MCT observations are meshed with the GO programs accepted by the Cycle 18 TAC. In the absence of Phase ΙΙ and accurate scheduling information, extended abstracts were made available on line by 1 February 2010, providing an overview of the proposed observations and science objectives of each program.
ConclusionThe Hubble MCT observing programs clearly represent a very significant investment of resources.
Observations for these programs will begin in Cycle 18, and will extend through at least Cycles 19 and 20. It is possible that scheduling constraints may push some observations in the M31 schedule to Cycle 21. Given this timeline, all three programs have been required to develop observing strategies that maximize the scientific return in the event that the project is interrupted. Each program will be required to submit regular progress reports, and will also be reviewed annually by the Institute Director and the STUC, with the latter representing the user community. Also, each program will be invited to make regular contributions to the Institute Newsletter to advertise its progress to the broadest audience.
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Optimizing Science with the Hubble Space TelescopeBrad Whitmore, [email protected]
One of the primary goals of the Space Telescope Science Institute (STScI) is to optimize science with the Hubble Space Telescope. This mantra has been with me since I joined the Institute some 27 years ago. It infuses everything we do at the Institute, from organizing the telescope
allocation process, to scheduling the telescope, to calibrating and characterizing the instruments, to making the data available through the archives. I was recently reminded of this by a presentation given by Riccardo Giacconi at the 20th anniversary Hubble Fellowship Symposium. He talked about the early days when he was the Institute’s Director, and about the “science system engineering” view we took to optimizing science from Hubble. He has expanded on this topic in his book, Secrets of the Hoary Deep: A Personal History of Modern Astronomy. In the context of the symposium, Giacconi explained that
this “system” approach even included the creation of the Hubble Fellowship program.
I recently became the Institute’s Project Scientist for Hubble. I was not expecting to apply for this position, but when the job advertisement came out and included statements like “explore potential science-driven enhancements that STScI can make to increase the impact of Hubble,” I found that it resonated. I felt it was a description of all the positions I have held over the years while at the Institute. In preparing for the job interview I started thinking about the various facets of optimizing science, not realizing that this was simply following the system-engineering approach that had been ingrained in me since arriving at the Institute.
I found myself thinking about a metric called “discovery efficiency,” which I first heard used by Holland Ford to characterize the improvement in science that the planned Advanced Camera for Surveys (ACS) would have over the existing Wide Field Planetary Camera 2 (WFPC2). The discovery efficiency is the product of the quantum efficiency (QE) times the field of view (FOV) of a detector. Unless a proposed new instrument improves the
discovery efficiency by at least an order of magnitude over its predecessor, it is hard to generate the enthusiasm needed to win over a review committee. In a recent example, the discovery efficiency in the ultraviolet for Wide Field Camera 3 (WFC3) is about 50 times better than WFPC2 (primarily due to the better QE) and better by a similar margin over the ACS (primarily due to the smaller FOV of the High Resolution Camera on ACS). The discovery efficiency of WFC3 in the infrared is also about 30 times better than NICMOS, due to a combination of both QE and FOV.
Figure 1: The footprint page from the Hubble Legacy Archive (www.hla.stsci.edu) for a search of 30 Dor. The positions of available images are shown for all instruments. In this particular case, a WFPC2 image has been selected by the user (the yellow outline).
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This concept of a science metric led me to develop the following framework for optimizing science with Hubble, based on three categories of performance: telescope capabilities, project turnaround time, and user bandwidth.
Component 1. Telescope Capabilities
The primary attributes defining the telescope capabilities are, of course, the capabilities of the instruments themselves. The QE and FOV of the detectors play major roles, but so do instrument modes—which ones are enabled, and how well are they calibrated, for example, at 10, 1, or 0.1% level? Often, hard tradeoffs are based on only partial information. For example, does the science that would result from enabling a rarely used mode justify the observing time and analysis effort to calibrate and characterize the mode?
Capabilities can also be improved by utilization factors, such as maximizing the scheduling efficiency, making good use of special observing modes like snapshots and parallels, and maximizing the lifetime of the instruments (health and safety issues are always paramount).
For example, starting in Cycle 17, we improved our utilization of Hubble by enabling a new way of performing pure parallel observations. It is clear that parallel observations have the potential to greatly enhance the overall science from the telescope, since in principle nearly twice as much data can be taken. In practice, the gain is somewhat less, since parallel observations cannot be attached to all primary observations.
There are two classes of parallel observations; coordinated parallels, where an observer includes the parallel observations in their own proposal, and pure parallels, where (before Cycle 17) the schedulers added parallel observations based on a generic algorithm (e.g., if in the galactic plane, use this set of filters, but if out of the plane, use a different set of filters). In practice, the science gains for the pure parallels have been relatively minor, partly because there was no “owner” who had specifically designed the observations for their project.
In Cycle 17, we changed the way we do pure parallels. The basic difference is that opportunities for deep parallel observations are now identified after the Phase I allocation (e.g., long primary COS and STIS exposures where several orbits are available for parallel observations of “blank fields”), and these opportunities are then matched to specific projects that have been allocated time for deep parallel observations.
Component 2. Project Turnaround TimeTypically, the turnaround time for a Hubble observing project—defined as the time from the initial
idea to the published paper—is several years. Our goal is to reduce the turnaround time by eliminating unnecessary delays in the timeline and improving the efficiency of data analysis. Observers should be using most of their time designing observations and interpreting the results, rather than waiting on the clock or calendar, or performing routine aspects of the analysis, like flat-fielding. Over the years, we have cut several months off the time delay between the selection of proposals and when observations actually start. Efficiency improvements have included providing high-quality data products via the calibration pipeline to reduce redundancy, and developing a set of generic analysis software tools for the community (Space Telescope Science Data Analysis Software, STSDAS). While scientists will always need to write some unique software code that is specific to their own project, the goal is to minimize the redundancy and provide standardized tools for the parts of the analysis that are repeated by a large number of users.
Reducing project turnaround times was the primary goal of developing the Hubble Legacy Archive (HLA) in recent years. The HLA makes it easier to determine whether some observation already exists in the archive, and provides general-use, value-added products that go a step beyond anything available in the past (e.g., combined astrometrically corrected images and mosaics, color images, and source lists). Many users can go directly to the data products they need and skip the whole proposal–observation–analysis cycle.
Figure 2: The color image from WFPC2 identified by the yellow outline in Fig. 1. For a complete description, see the HUBBLEOBSERVER FACEBOOK page (www.facebook.com/pages/HubbleObserver/276537282901/; May 24, 2010 post).
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Component 3. User BandwidthThe third component of our science optimization framework is “user bandwidth.” While this component is
more nebulous than the others, we might paraphrase it as the attempt to find the best mix of proposals from the broadest spectrum of observers for as many years as possible. The Telescope Allocations Committee (TAC) is charged with recommending the highest-quality science program. Over the years, the Institute has developed a set of procedures and guidelines to ensure a good mix of small proposals (allowing quick, innovative research) and large proposals (survey-type studies involving large statistical samples). Similarly, we strive to have a diverse set of users, including theorist and observers, experienced and novice users with fresh ideas, a wide range of scientific disciplines, and a multi-wavelength user base.
Another aspect of bandwidth relates to science opportunities. We want the Calls for Proposals to shape the allocation of Hubble to achieve the best total science. We want to keep Hubble operating long enough to overlap with the Webb, which would provide powerful synergy. Also, we want to ensure that Hubble data will be readily available to future generations via the archives.
An example of a recent development in this area is the Multi-Cycle Treasury Program (MCTP), an extension of the original “Key Projects,” which were completed in the early cycles (e.g., Distance Scale, QSO Absorption Lines, and Medium-Deep Survey), and more recently, the Treasury Program. The goal of MCTP is to make it possible for very large projects to compete more effectively by designating a certain fraction of the observing time for them.
First Thoughts & What You Can DoOther frameworks for optimizing Hubble science
can and have been developed, of course. One example is an end-to-end or cradle-to-grave approach, where each step in the project lifecycle is scrutinized and optimized (i.e., proposal submission → allocation → phase ΙΙ development → scheduling → calibration → archiving → analysis → publication). This approach largely reflects how the Institute is organized, with separate branches for most of the steps. The framework outlined above is designed to take a somewhat orthogonal approach, which may identify opportunities that may have been missed in the past and might now be explored.
The focus of this framework is more on the long-term rather than day-to-day considerations, especially the user bandwidth component. For example, it is important to ensure that our data products are compatible with the Virtual Observatory, and ready for full integration. This bandwidth consideration will
ensure that data products will be easily available and fully useful for future generations of astronomers. As another facet of this goal, we must capture as much documentation describing the instruments and calibration of the data as possible, to ensure current knowledge and expertise is not lost.
Another innovation is the focus on project turnaround time, which promotes a user viewpoint. For example, developing a tool or a data product that greatly simplifies a common analysis step for many users might reduce the average turnaround time, and hence, have a very high science impact.
One important factor in optimizing science with Hubble is keeping our users informed. This Newsletter is one channel. On shorter timescales, we use e-mail or post items on the Institute web pages. Two new methods are the HUBBLEOBSERVER FACEBOOK and TWITTER pages, which enable observers to stay informed about the latest relevant Hubble information without requiring them to scout it out. Examples of topics highlighted in the past few months have ranged from proposal statistics, instrument news, and recent press releases, to Data Release 4 of the HLA.
One of the main reasons for this article is to elicit your help in thinking about potential ways to optimize the science coming from Hubble, both now and for the future. If you have some pet idea—or perhaps reading this has inspired some new possibility—please pass it along for consideration ([email protected]). While we will be scaling back our level of support for Hubble over the next several years as we ramp up to support Webb, we are always looking for new ideas where the cost-benefit ratio is advantageous. I will plan to come back in a year or so and report on changes we have made based on your feedback.
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Figure 3: A snapshot of the HUBBLEOBSERVER FACEBOOK page, taken in April 2010.
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Cosmic Origins Spectrograph NewsAlessandra Aloisi, [email protected], for the COS team
T he Cosmic Origins Spectrograph (COS) was installed on Hubble during Servicing Mission 4 (SM4) on May 16, 2009. Since then, a vigorous scientific program has been underway using COS’s unique ultraviolet spectroscopic capabilities (for an example, see Fig. 1).
By the end of June 2010, the far-ultraviolet (FUV) detector on COS had been used to make ~1300 spectroscopic science exposures of external targets, and the near-ultraviolet (NUV) detector had been used for ~550. An additional ~1000 exposure sequences were performed for target acquisitions, and ~970 internal calibration exposures had been taken.
The topics of COS science papers that have already appeared in refereed journals include a supernovae remnant (France et al. 2009, ApJ, 707, 27), a massive run-away star from the extreme star-forming region 30 Doradus in the Large Magellanic Cloud (Evans et al. 2010, ApJ, 715, L74), the accretion disk of a young brown dwarf star in our Galaxy (France et al. 2010, ApJ, 715, 596), high velocity clouds (Lehner & Howk 2010, ApJ, 709, 138), the warm intergalactic medium (Danforth, Stock, & Shull 2010, ApJ, 710, 613), and transiting extrasolar planets (France et al. 2010, ApJ, 712, 1277; Fossati et al. 2010, ApJ, 714, L222). Many other COS results have been presented in conference proceedings and preprints.
The initial on-orbit characterization of COS was performed during the servicing mission observatory verification (SMOV) activities, which were completed at the end of September 2009. This milestone marked the commissioning of COS for observations by the astronomical community. At that time, COS operational responsibilities were handed off to the Institute from the COS instrument development team (IDT), which is led by the principal investigator, Dr. James Green of the University of Colorado.
Since commissioning, the Institute has implemented several calibration enhancements aimed at optimizing COS science. We have initiated these enhancements in the Cycle 17 calibration program, which is currently underway. We monitor the dark-current, flux, and wavelength calibration of the instrument. In Cycle 17, we also put special emphasis on aspects of COS calibration which are expected to be problematic, or which SMOV did not fully explore, such as (1) throughput of the FUV channel below 1150 Å, (2) extension of the COS FUV coverage down to 900 Å at higher resolution using two new G130M settings, (3) characterization of the geocoronal Ly-α emission, (4) improvements in the flat-field correction for the COS FUV detector, (5) checks on the zero point of the wavelength calibration for a number of settings, and (6) re-determination of the best focus position for the G140L grating. We are executing most of these special calibrations in the second part of Cycle 17 (spring and summer 2010).
On-orbit monitoring of the COS NUV and FUV throughput has produced a few surprises. Before launch, the bare-aluminum gratings G225M and G285M in the NUV channel showed a wavelength-independent degradation of throughput of about 1.6% and 4.5% per year, respectively. This degradation had been attributed to the growth of a thin oxide layer on the grating surface during the nitrogen purge that kept humidity out of the instrument during ground testing. Expectations were that this growth would have stopped once on orbit and that the throughput decline of the G225M and G285M gratings would have ceased, but this is not the case.
We use two different approaches to monitor the NUV gratings in the Cycle 17 calibration program. For continuity, we continue to execute—in the same cadence—the grating efficiency test that was executed every six months from 2003 to launch. This procedure uses the internal platinum-neon lamp. The second approach is to regularly observe a photometric standard star. Both these approaches indicate that the
Figure 1: Variation in the outflow of material from Markarian 817, a nearly face-on spiral galaxy. The outflow is powered by a massive black hole at the center of this active galaxy. In 1997, the Goddard High Resolution Spectrograph detected an out-flowing cloud of hydrogen gas that does not appear in a 2009 COS spectrum using the G130M grating. Apparently, the cloud was driven out in the intervening 12 years, probably by an outflow of material from the galaxy. The cloud’s Lyman-alpha (Ly-α) line occurs at 1236 Å, which is blue-shifted with respect to the Ly-α line from the general reservoir of hydrogen in Markarian 817, which occurs at ~1252 Å. The image of Makarian 817 is a Wide Field Camera 3 composite image in the F438W, F555W, F814W and F680N filters, taken on August 2, 2009.
throughput of the bare-aluminum gratings continues to decline at a rate 2–3 times higher than before launch (see Fig. 2).
While the continued on-orbit degradation of the NUV bare-aluminum gratings G225M and G285M was not anticipated before launch, this effect only marginally impacts a very limited amount of COS science. The gratings are used very little during Cycle 17 (about 3% of the total COS time). They still provide a throughput that is slightly higher or comparable to the throughput of the STIS medium-resolution gratings covering the same wavelength range (E230M and G230M).
The NUV magnesium-fluoride-coated gratings G185M and G230L showed no evidence of significant throughput changes over time before launch, and continue to show no changes in orbit.
We also monitor the FUV gratings periodically as part of the COS Cycle 17 calibration program. The throughput of these gratings is declining faster than we expected. We have monitored the G140L grating most extensively, with data taken at a monthly cadence since the beginning of on-orbit operations. We have observed the other two FUV gratings, G130M and G160M, only quarterly before March 2010, but monthly since then. The degradation in throughput is wavelength-dependent, with the longest wavelengths manifesting the largest decrease. Also, the same throughput loss is observed in the same wavelength region covered by different gratings, independently of the pixel location in the dispersion direction. These two aspects of the FUV throughput degradation suggest a detector effect—particularly, aging of the cesium-iodide photocathode. This aging is not localized to the most heavily used areas of the FUV detector. That is, it is not related to the fluence or the total number of photons that hit the detector, but is a global effect. The rate of the FUV throughput loss is between 3% and 13% per year, depending on the wavelength (see Fig. 3). This rate is higher than ever observed in any other cesium-iodide photocathode flown on Hubble—or on any other space-astronomy mission. This difference could be due to contamination, because the COS FUV detector is windowless, instead of being a sealed tube. The Institute’s COS team, in collaboration with the COS IDT and the Hubble project at Goddard Space Flight Center, is currently investigating the physical causes of the FUV throughput loss and possible mitigating actions. Despite this loss, COS is still the most sensitive spectrograph ever flown on Hubble, being a factor of 10 to 30 more sensitive than the Space Telescope Imaging Spectrograph in the FUV spectral range.
The decline in throughput of all the FUV gratings and the two bare-aluminum NUV gratings (see Fig. 4) have been included into the COS exposure time calculator (ETC). ETC 18.2 was released to the public in April 2010 to support preparation of Phase ΙΙ of the COS Cycle 18 approved programs. This version
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Figure 2: Throughput degradation as a function of time for the two NUV bare-aluminum gratings. The data are from the Cycle 17 COS calibration monitoring program 11896. Left: data from G225M at the central wavelength of 2414 Å. Right: data from G285M at the central wavelength of 2739 Å. The external target used for these observations is G191B2B, a white dwarf that is a Hubble photometric standard star. In each panel, the three parts of the NUV spectra are represented from top to bottom (to accommodate the NUV detector format, the COS NUV spectrum is split into three non-contiguous stripes, each of which covers a relatively small range in wavelength). For each part, the net counts of each epoch are normalized to the net counts of the first epoch.
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uses the measured trends in throughput extrapolated to the mid-point of Cycle 18 (March 2011).The monitoring of the COS NUV dark current is another area that produced unexpected results. The
initial SMOV measurement of about 6 × 10-5 counts pixel-1 s-1 was lower than the pre-launch predictions of 3.7 × 10-4 counts pixel-1 s-1. Since that time, however, the dark current has continuously increased. By late June 2010, it had risen to a level of about ~3.5 × 10-4 counts pixel-1 s-1. It appears to be rising linearly with time at a rate of ~2.8 × 10-4 counts pixel-1 s-1 per year. In addition to this trend, there also appears to be a correlation between the dark rate and the detector temperature (see Fig. 5). It is possible that the increasing dark current is due to window phosphorescence, similar to that observed in the STIS NUV MAMA detector. However, the COS NUV detector dark rate is still several times lower than both the pre-SM4 STIS NUV dark rate (~1.3 × 10-3 counts pixel-1 s-1) and the current enhanced STIS NUV dark rate (~4 × 10-4 counts pixel-1 s-1 ). The current value of the COS NUV dark current has been included into the COS ETC version 18.2.
Calibration of FUV flat fielding is under investigation. While FUV exposures are currently not corrected for flat field, data retrieved from the archive after March 2010 are calibrated with CALCOS in a way that the bad detector regions and grid wires are properly masked when combining data taken at different FP-POS positions into an X1DSUM spectrum. While this process cannot remove the ~5% pixel-to-pixel variations of an FUV flat field, it does a reasonable job removing the fixed pattern noise due to the grid wires. The Institute, in collaboration with the COS IDT, is working to release a post-calibration tool to combine data taken at different FP-POS positions into one summed spectrum, possibly in summer 2010. This tool would simultaneously fit the data with an initial guess of the flat field and of the science spectrum as inferred from the data, and will continue to iterate this process until the best fit is found for both. Also, we expect to fully integrate the one-dimensional flat-field corrections for FUV observations into CALCOS. This awaits the full analysis of the on-orbit data from Cycle 17 calibrations (summer 2010).
The Institute has also been working on other aspects of COS operations. The tabulated position of the COS aperture relative to the Fine Guidance Sensors (FGSs) was updated in the science instrument aperture file, based on on-orbit measurements of an astrometric target at the beginning of March 2010. The revised
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Figure 4: Slope of the throughput degradation as a function of wavelength for all COS FUV and NUV gratings.
Figure 3: Throughput degradation as a function of time for the two medium-resolution FUV gratings. Left: data of the star WD0947+857 using the G130M grating at the central wavelength of 1327 Å are plotted. Right: data of the star WD1057+719 using the G160M grating at the central wavelength of 1600 Å are plotted. In each panel, the two parts of the FUV spectra are represented from top to bottom (the COS FUV detector consists of two independent segments with a small physical gap between them). For each part, the net counts of each epoch are normalized to the net counts of the first epoch.
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aperture position should be accurate to about 0.03 arcsec. The accuracy of COS’s initial pointing should now be limited by the accuracy of the individual stellar positions from the guide star catalog and of the user-supplied coordinates—not by the accuracy of the COS-to-FGS offset. Following this update, monitoring of target acquisitions has confirmed that the targets are usually well centered into the COS aperture. The Institute has revised the policy requiring that each visit starts with an ACQ/SEARCH target acquisition mode. (ACQ/SEARCH performs a search in a spiral pattern by executing individual exposures at each point in a square grid pattern). In most circumstances, observers with approved Cycle 18 Phase Ι programs will be allowed to drop ACQ/SEARCH and use the time previously allocated to this target acquisition mode for longer integrations of the science exposures.
An updated version of the COS pipeline (CALCOS v.2.12) was released to the public in April 2010 as part of OPUS build 2010.1b. This new version encompasses a variety of bug fixes and improvements, including a number of changes to the processing of spectra from the wavelength calibration lamp. This update should make the determination of the observational wavelength-scale zero-points more robust and reliable.
The calibration reference files used by CALCOS were also updated with on-orbit performance information of COS. This information includes the variations in throughput for both the NUV and FUV channels. General observers who wish to take full advantage of the new on-orbit calibrations should re-retrieve their proprietary data from the archive through the on-the-fly recalibration. In particular, the reference file for the screening of the pulse-height amplitude of each detector event (5 bits with values ranging from 0 to 31) was updated to use a new pulse-height range between 4 and 30. This change only affects FUV data taken in TIME-TAG mode, where a pulse height (or total charge collected for each photon striking the
detector) is saved along with the x–y position of each photon event and the arrival time. This allows users to lower the detector background and remove several spurious features seen on segment B in particular, with only a minimal loss of sensitivity (a few percent). Also, FUV and NUV dispersion reference files and lamp templates were updated with SMOV data. This update substantially improves the zero-point of the wavelength calibration for most COS spectroscopic modes, and allows an observer to achieve an accuracy of the on-orbit absolute wavelength calibration that meets the requirements (15 km s-1 for NUV and FUV medium-resolution gratings, and 150 km s-1 and 175 km s-1 for G140L and G230L, respectively).
The Institute is still investigating the nature and frequency of some residual localized distortions, particularly in the FUV wavelength scale, which are not corrected by the current dispersion solution.
The COS Instrument Handbook for Cycle 18 by Dixon et al. was published on January 5, 2010. The Institute’s COS instrument website (http://www.stsci.edu/hst/cos) provides this handbook, as well as the first version of the COS Data Handbook, many instrument science reports summarizing the performance of the instrument in SMOV and early Cycle 17, an updated version of the instrument brochure, and a wide variety of other up-to-date user-support information.
Figure 5: Dark current (top panel) of the COS NUV MAMA as a function of time from SM4 until the end of June 2010. The dark current is still increasing linearly with time, at a rate of ~2.8 × 10-4 counts pixel-1 s-1 per year (solid line in the top panel). Notice that the dark current also shows some correlations with the temperature of the MAMA tube (bottom panel).
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Enabling New Science with WFC3 Jason Kalirai, [email protected], John MacKenty, [email protected], and the WFC3 Team
T he new Wide Field Camera 3 (WFC3) on Hubble is in full scientific operation! Still in its first year, the instrument is quickly emerging as one of astronomy’s most important tools, and is likely to answer a wide range of scientific questions about the cosmos. In the first weeks of
science operations, WFC3 captured images of an impact on Jupiter and detected the highest redshift galaxies ever observed. Over the coming year, about half of all Hubble observations will use the new instrument. In our local cosmic neighborhood, WFC3 will perform a wide variety of studies, including characterization of planets, brown dwarfs, and hydrogen-burning stars. Beyond, it will improve our understanding the formation of stars and galaxies, map cosmological relationships, and perhaps reveal the fate of the universe.
WFC3 in Orbit: First Performance Results
The cameras on Hubble have profoundly influenced the course of modern astrophysics. Until now, the Wide Field Planetary Camera 2 (WFPC2), the Near Infra-Red Camera and Multi-Object Spectrometer (NICMOS), and the Advanced Camera for Surveys (ACS) provided the deepest and most sensitive images ever of stellar populations in the universe. Observing programs like the deep imaging surveys of star clusters and the Hubble Deep Fields have clarified the basic processes that operate in the formation and evolution of stars and galaxies. WFC3 is the next leap forward. Its ultraviolet-visible (UVIS) and the infrared (IR) cameras both offer fields several arcmin wide. Both have ultra-sensitive detectors: CCD in UVIS and mercury-cadmium-telluride in IR. Both deliver high resolution, with spatial scales of 0.04 arcsec in UVIS and 0.13 arcsec in IR. Together, the two cameras contain 77 narrow-, medium-, and wide-band filters—and 3 grisms. WFC3’s combined capabilities allow panchromatic imaging and spectroscopy over a 0.2–1.7 micron wavelength range. It offers substantially higher imaging sensitivity and resolution than previous instruments in the UV and IR.
Following its installation in Hubble in May 2009 by the crew of STS-125, the WFC3 team conducted a comprehensive checkout and calibration program to measure the on-orbit response of the instrument and characterize its performance. Calibration data from the first 10–12 weeks of operation have been fully analyzed and reported in a series of 30 instrument science reports (ISRs, available at http://www.stsci.edu/hst/wfc3/documents/ISRs/ ). These calibrations used standard stars and star fields, as well as internal lamps. This effort established the optical alignment, pointing corrections, geometric distortion, point-spread function (PSF), and photometric sensitivity and stability. For the most part, these measurements confirmed our ground-based understanding of the detectors. However, as a pleasant surprise, on-orbit observations of photometric standard stars indicate that the instrument is 10–20% more sensitive than expected—across the entire UV–VIS–IR wavelength range.
For specific scientific investigations with the newly refurbished Hubble, users often ask, “Which instrument should I use?” For many projects, the most important metric is the limiting magnitude reached in a given exposure time. Figure 1 compares Hubble imaging instruments in terms of this metric.
At UV and VIS wavelengths, WFC3 offers both advantages and disadvantages compared to ACS. For example, WFC3 offers 62 UVIS filters, so some studies may be possible only on WFC3. Nevertheless,
Figure 1: The five-sigma, limiting, AB magnitude of a point source reached in 10 hours of exposure with various Hubble imaging instruments. The calculation assumes an optimal aperture for extraction. Over almost the entire wavelength range probed by Hubble instruments, WFC3 offers the highest sensitivity.
Hubble - Limiting Magnitude in 10 Hours
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the WFC3 field of view is 40% smaller than that of the ACS wide-field camera (WFC). For this reason, survey-type programs, which must cover large regions of the sky, may prefer ACS. In terms of VIS sensitivity, although the throughput of the WFC3/UVIS camera is somewhat lower than ACS/WFC, the new instrument offers (1) better sampling of the PSF (20% smaller pixels and on-axis alignment within the telescope); (2) 50% lower read noise; (3) much lower dark current; and (4) negligible charge transfer efficiency (in the near term). Taking all of these factors into account, the point-source limiting magnitude reached by WFC3 and ACS in the V band is similar, and ACS slightly outperforms WFC3 in the I band. This comparison illustrates Hubble’s unprecedented capability for simultaneous ultra-sensitive, high-resolution, wide-field imaging of astrophysical sources using both instruments.
New WFC3 observations of the star clusters 47 Tuc and Omega Cen have provided geometric distortion solutions of sufficient quality to support the Institute’s MultiDrizzle image-combination software. Starting in late January 2010, this software has been at work in the OPUS pipeline. Re-processed data will include these calibrations. Users should be aware that both these calibrations and the software—which by their nature could not be fully exercised prior to flight—are still undergoing improvements and bug fixes. Please consult the Institute’s WFC3 (http://www.stsci.edu/hst/wfc3/ ) and MultiDrizzle (http://www.stsci.edu/hst/wfc3/tools/MultiDrizzle/ ) websites for additional information.
For the CCD detector, in-flight bias files are available, and since the ground calibrations, the flat fields appear stable. The IR darks and flats show some variations and improved in-flight darks are now available, with flats coming in summer 2010. Telescope backgrounds and detector radiation effects are close to our pre-flight expectations, as documented in the Cycle 18 version of the WFC3 Instrument Handbook.
The WFC3 team has supported the astronomical community and Hubble users by making available the latest calibration files, such as biases, flat fields, and distortion solutions. They can be found on our web site. After some additional validation, they will be implemented in the automated reduction pipeline. The team made appropriate modifications to the throughput tables that characterize the sensitivity. Also, they updated the image headers and the exposure
time calculator, and published the new photometric zero points—both in ISRs and on the instrument web page (WFC3 ISR 2009-30; WFC3 ISR 2009-31; http://www.stsci.edu/hst/wfc3/phot zp lbn/).
The WFC3 team is contacting Cycle 17 general observers who have acquired data from the instrument. We are particularly interested in feedback to identify new issues and to define future calibration and characterization activities to maximize the instrument’s scientific return. We are in the process of executing a more detailed calibration for Cycle 17.
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WFC3from page 29
Figure 2: Snapshots of four recent WFC3 observations spanning ultraviolet, optical, and infrared wavelengths at high resolution and over large fields of view. Top-left: The “butterfly” nebula illustrates the process of stellar death in an intermediate-mass star. Top-right: Stephan’s Quintet showcases interacting galaxies in the distant Universe. Bottom-left: Omega Cen is a dense collection of millions of stars that can be individually resolved to study stellar evolution and star cluster formation. Bottom-right: A stellar jet in the nearby Carina Nebula.
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A Bright Future for WFC3The first on-orbit measurements of the performance of WFC3 have exceeded expectations. The
new scientific investigations using WFC3 in Cycles 17 and 18 will provide unprecedented constraints on our understanding of a wide range of astrophysical problems, from detailed studies of the initial mass function and its dependencies on age, metallicity, and environment, to investigations of global galaxy structure and evolution, to research on dark matter, dark energy, and cosmology with type Ia supernovae. Our confidence in WFC3’s ability to accomplish the scientific goals of such research projects is based on our understanding of its performance and the quality of its calibration, which we expect will continue to improve over the coming year.
ACS Status Linda Smith, [email protected], David Golimowski, [email protected], and Norman Grogin, [email protected]
T he Wide Field Channel (WFC) and the Solar Blind Channel (SBC) of the Advanced Camera for Surveys (ACS) are continuing to perform well after the repairs made during Servicing Mission 4 (SM4). All aspects of the WFC performance were checked during the servicing mission
observatory verification (SMOV) period. The replacement electronics have given the WFC detectors new characteristics as described below.
The replacement CCD electronics box (CEB-R) is equipped with two correlated-double sampling (CDS) modes (clamp and sample, dual-slope integration), which can be used to measure the charge accumulated by each pixel during read out. The clamp-and-sample mode was used successfully in the old CEB, but the dual-slope integrator (DSI) offers lower read noise at the expense of more bias structure. Post-SM4 image analysis confirms that the DSI yields significantly lower read noise (3.9–4.7 compared to 5.5 electrons), and that bias frames exhibit a 5–10 digital-number (DN) gradient spanning the rows of each image quadrant. The bias gradient is stable and can be precisely removed during normal image reduction and processing. Consequently, the DSI has been selected as the default CDS mode for post-SM4 observations.
Another characteristic of the new WFC electronics is the presence of faint horizontal stripes that extend along the rows of the CCD and across the quadrant boundaries. The stripes are constant along each row of pixels, but they are not stable from frame to frame. The stripes are caused by low-frequency (1 mHz to 1 Hz), 1/f-noise on the reference voltage, generated by the application-specific integrated circuit (ASIC) used to offset the pixel signal after CDS is performed. The stripes are present in all WFC calibration and science images, regardless of CDS mode. The contribution of the stripes to the global read noise statistics is small (the peak-to-peak deviation is approximately 2 DN), but the correlated nature of the noise may affect photometric precision for very faint sources. The ACS team has developed algorithms for removing the stripes from calibration and general science images, and we are in the process of releasing these algorithms to the community as standalone software packages that operate on the images independently of the CALACS software package.
The level of ACS/WFC amplifier crosstalk after SM4 is the subject of a recent instrument science report (ISR 2010-02) by A. Suchkov, N. Grogin, M. Sirianni, E. Cheng, A. Waczynski, and M. Loose (http://www.stsci.edu/hst/acs/documents/isrs/isr1002.pdf). When each quadrant of the two WFC CCD detectors is read out, electronic crosstalk between the amplifiers induces faint, typically negative, mirror-symmetric ghost images on the other three quadrants. The effect is strongest for high-signal pixels. Analysis of pre-SM4 crosstalk showed that its impact on ACS/WFC science is not significant and can be ignored in most science applications. Analysis of the crosstalk after SM4 shows that the crosstalk due to low-signal pixels is much weaker than before SM4 and does not produce ghosts similar to those seen in pre-SM4 images. For high-signal pixels, we find substantial differences between the gain = 1 e¯/DN and gain = 2 e¯/DN cases. For the default gain setting of 2, the crosstalk is similar to what it was before SM4: up to 5–8 e¯ per pixel on the same CCD. For gain = 1, the crosstalk is ~100 eˉ per pixel for saturated pixels on the same CCD, which is more than an order of magnitude above the pre-SM4 level. The crosstalk from saturated pixels is ~20–30 e¯ per pixel on the other CCD, which is also much higher than it was before SM4.
STIS Update Charles Proffitt, [email protected]
S ince its repair during Servicing Mission 4 (SM4), the Space Telescope Imaging Spectrograph (STIS) has resumed its role as an important part of Hubble’s instrument complement. Here we discuss recent changes in the detector background for STIS’s Charge Coupled Device (CCD)
and near-ultraviolet (NUV) Multi-Anode Microchannel Array (MAMA) detectors.The STIS CCD detector continues to accumulate radiation damage. In March 2010, the median
CCD dark current was 0.014 eˉ/pixel/sec near the top of the detector, and 0.019 eˉ/pixel/sec near the center. About 4% of the pixels are considered to be “hot” pixels, as they now show a dark current of more the 0.1 eˉ/pixel/sec.
The biggest STIS surprise after SM4 was the strongly elevated dark rate in the NUV MAMA detector. This dark rate is attributed to a phosphorescent glow from depopulation of meta-stable states in the MgF2 window in front of the detector. These meta-stable states are excited by charged-particle impacts. When the detector was initially turned on after SM4, the dark rate was approximately 0.013 counts/pixel/sec—about ten times higher than it had been before the 2004 failure of STIS. At first, this excess dark rate was declining with a time scale of about 100 days, and we had hoped that by the start of Cycle 18 it might have decreased to levels close to what had been seen in 2004. Nevertheless, over the last few months it has become apparent that the time scale for this decline has lengthened considerably. As of April 2010, the mean STIS NUV MAMA dark rate was about 0.0044 counts/pixel/sec, and the eˉ folding time for further decreases appears to be more than a year. Figure 1 shows the measured values of the STIS NUV MAMA dark rate since SM4. It appears that the number of excited states with long time scales for decay greatly increased during the years that STIS was inoperative, and it may take considerable time before a new equilibrium is reached. In recent weeks we have observed almost no decline in the overall dark rate.
The open circles in the upper panel show the measured values of the STIS NUV MAMA dark rate taken since the detector was restored to operation in August 2009. The + symbols show the predictions of a two-term empirical fit of the form A¹eˉE¹/T eˉ t/τ¹ + A²eˉE²/T eˉ t/τ², where T is the temperature of the detector tube. A good fit can be found for τ¹ ~ 40 days and τ² ~ 400 days. The lower panel shows the residuals of this fitting formula.
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Continuedpage 34
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Webb Update Massimo Stiavelli, [email protected]
D eveloping the James Webb Space Telescope is now in full swing. Components representing 14% of
the mass of the observatory have been fabricated, and other parts for 47% of the mass are under construction. The remaining 39% of the mass will be completed over the next two years. Important components of the observatory—and, indeed, the mission itself—recently passed major reviews. A test of figuring primary-mirror segments was a success. With these milestones accomplished, the phase of designing and analyzing Webb winds down, and the era of integrating and testing ramps up.
In February 2010, the demonstration model of the Near Infrared Spectrograph was delivered to the Goddard Space Flight Center to begin testing. The large clean room used for work on Hubble servicing missions is now being used for Webb. NASA has installed a “Webb cam” in the clean room to provide continuous coverage of the assembly of the Webb instruments and telescope (http://www.jwst.nasa.gov/webcam.html).
Passed ReviewsIn October 2009, Webb’s Optical Telescope Element (OTE) passed its critical design review (CDR).
The OTE comprises the primary, secondary, tertiary, and fine steering mirrors.In January 2010, the Webb sunshield passed its CDR. The sunshield is a critical component of the
observatory, as it enables the telescope optics and instruments to radiatively cool down to 40 K. At launch, the sunshield will be folded, but will deploy to its full tennis-court size en route to L2. NASA had delayed manufacturing the sunshield so the design team could work through several prototypes before selecting the design that offered the greatest deployment reliability and protection during integration and launch.
Figure 1: View of the backside of a six-mirror segment assembly being readied for testing at the XRCF at the Marshall Space Flight Center. Visible are the honeycomb light-weighting of the mirror segments and the cabling for the mirror actuators, which correct the shape of the primary.
Figure 2: Front view of a six-mirror segment assembly being inspected before testing at XRCF..
In April 2010, Webb passed its mission CDR, which was held at Northrop Grumman’s Redondo Beach facility near Los Angeles. Over the course of several days, 1,854 viewgraphs were presented by the leads of all subsystems. The final conclusion was that Webb's development is on track, despite its complexity.
Verification of Figuring Method Ensuring that the primary mirror
segments have the correct figure when cooled to the 40 K operating temperature is a major challenge. The segments are polished at room temperature to a shape that is not the desired flight shape, but the mirrors will deform to the correct shape when cooled to flight temperatures. This strategy requires extensive numerical simulations and iterative polishing and testing. In the final stages, the mirror segments circulate around the country: First, they are figured, polished, and measured at Tinsley Laboratories in California. Next, the segments travel to Colorado for the support structures to be installed at Ball Aerospace Technology Corporation. Next, the units travel to Alabama for optical measurements at cryogenic temperatures at the X-Ray and Cryogenic Facility (XRCF) at the Marshall Space Flight Center. Then the cycle is repeated, with further polishing at Tinsley, remounting at Ball, and retesting at Marshall, until the required optical figure is achieved.
As of January 2010, this complex process of figuring Webb’s primary mirror segments was tested and verified, when a flight spare successfully completed this polishing and testing cycle. Many lessons were learned on this pathfinder program, which should substantially reduce the polishing and testing times for the remaining segments. Many of the segments are ready for testing at the XRCF.
Figure 4: The six-mirror segment assembly in position inside the vacuum chamber at the XRCF. The crew poses before the chamber is closed and testing begins.
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Webb Updatefrom page 33
Figure 3: The six-mirror segment assembly being moved into position inside the XRCF vacuum chamber. The chamber walls are visible at the edges of the picture.
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Wavefront Sensing and Control on the James Webb Space Telescope Roeland P. van der Marel, [email protected]
T he optical telescope element (OTE) of the James Webb Space Telescope has a three-mirror anastigmat, f/20 design, consisting of a primary, secondary, and tertiary mirror. A fine-steering mirror provides line-of-sight stabilization. The design of the OTE was chosen to provide a high quality
image to the integrated science instrument module (ISIM), which houses the Webb science instruments.The mirrors are made of beryllium, which has an extremely small variation in its coefficient of thermal
expansion over temperatures of 30–80K. This makes the telescope optics intrinsically stable for small temperature variations. A thin gold coating provides high infrared reflectivity over a broad wavelength range, from 0.6 to 29 microns.
All the optical elements of the OTE are in advanced stages of production. Cryo-polishing has been completed for an engineering test unit of a primary mirror segment. It has achieved an excellent wavefront error, which demonstrates that the requirements for Webb to deliver diffraction-limited performance at a wavelength of 2 microns can be met.
The primary mirror consists of 18 semi-rigid, hexagonal mirror segments. Together, these make up a quasi-hexagonal, 6.5 m diameter, two-ring configuration with a collecting area of 25 square meters. The segments are attached to a stable, rigid, graphite-composite backplane structure. At launch, the primary mirror is folded on two chords, allowing it to fit in the fairing of the Ariane launch vehicle. Similarly, the secondary mirror is attached to a deployable tripod support structure, which latches into position after launch.
The OTE deploys over the course of a week, starting approximately five days after launch. Then a 1–2 month commissioning process to optimize the telescope image quality begins. The goal of this process is to align the primary segments into a co-phased state, and to align the primary and secondary mirrors with the aft optics system, which is fixed and houses the tertiary mirror, the fine-steering mirror, and a central baffle.
To align the telescope, each primary mirror segment is mounted on three bipods (a hexapod) to form a kinematic attachment to the backplane. Six actuators with both coarse- and fine-positioning capability adjust the lengths of the hexapod’s legs. This arrangement permits six degrees of freedom to be adjusted independently: x- and y- position, piston, tip, tilt, and clocking. The secondary mirror also has six actuators, permitting the same kind of control. For each of the primary mirror segments, an additional (seventh) actuator controls the radius of curvature.
In total, there are 132 controllable degrees of freedom in aligning the OTE. The process by which these degrees are used to optimize the Webb image quality is called wavefront sensing and control (WFS&C). Unlike the case for ground-based adaptive optics systems, WFS&C is not a real-time process that runs autonomously on the telescope. For ground-based observations, the short characteristic timescales of atmospheric turbulence dictate rapid sensing and correction. By contrast, Webb operates at the second Sun-Earth Lagrange point, L2, in an environment with no atmosphere and little gravity. The relevant timescales for WFS&C are dictated by slow thermal drifts, which occur on day-to-week timescales. Therefore, the cheapest and most reliable approach is to obtain data through the regular, pre-planned observing methods, downlink of the data, analysis on the ground, and uplink to the telescope of any commands to move actuators.
Immediately after OTE deployment, the telescope point-spread function (PSF) consists of 18 separate, out-of-focus images, one from each primary mirror segment. The first OTE commissioning steps use a bright star to determine and calibrate the telescope line of sight, and to locate and identify the image of each individual segment. The mirror segments can then be tilted to align the 18 separate images into a single image. The
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Figure 1: Deployment sequence for the primary and secondary mirrors of the Webb telescope. The aft optics system is housed in the primary mirror gap, and includes the central baffle. Following deployment, a sequence of wavefront sensing and control activities bring the telescope into focus.
wavefront superposition thus obtained is incoherent. As a result, the PSF at this stage has a width typical of a single (1.32 m flat-to-flat) mirror segment.
To obtain the 6.5m diffraction-limited performance, it is necessary to co-phase the segments. This involves two main steps, each of which uses dedicated hardware within the Near-Infrared Camera (NIRCam). These steps are called coarse phasing and fine phasing.
Coarse phasing uses dispersed Hartmann sensing. This process uses grisms to create wavelength-dependent interferograms based on the light reflected by adjacent mirror segments. This allows identification of large piston errors between segments, which would then be corrected.
Fine phasing is done using a set of weak lenses, which can be chosen to yield images with five defocus settings: –4, –8, 4, 8 and 12 waves at 2.12 micron. Images thus obtained can be analyzed with focus-diverse phase retrieval algorithms, which yield a map of the optical path difference (OPD) over the telescope pupil. The specific algorithm used for Webb is the “hybrid diversity algorithm” (HDA), which is a variation of the well-known Gerchberg-Saxton scheme, with an additional outer loop in the process to provide phase-unwrapping and robustness even with large phase errors.
The phase-retrieval process requires amplitude information for the pupil, which is also obtained using dedicated NIRCam hardware. A Pupil Imaging Lens (PIL) provides the required imaging. The resulting data can also give insight into vignetting or other alignment problems.
Once an OPD map has been determined from NIRCam imagery, its low-spatial frequency content is corrected by moving actuators appropriately to reposition the segments. Mid- and high-spatial-frequency figure errors, which may be caused by manufacturing errors within a segment, cannot be corrected by this process. Nevertheless, these errors are bounded by robust error budgets in the manufacturing process, which ensures diffraction-limit performance. Furthermore, these uncorrectable errors are stable and can be accurately characterized during telescope integration and testing (I&T). This enables accurate prediction and characterization of the post-commissioning PSF.
Most WFS&C steps are performed at a single field point in NIRCam. During the initial alignment, however, multi-field, multi-instrument wavefront sensing is also performed in order to remove ambiguities that might
arise when using NIRCam alone. In principle, these WFS&C steps can be repeated as necessary during the Webb mission.
After OTE commissioning has been completed, a maintenance process of WFS&C executes for the duration of the mission. In its cooled, equilibrium state, the primary mirror experiences a large temperature gradient (some 20–30 degrees over the 6.5 m aperture) in the direction away from the sunshield. This gradient is stable, and any distortion that it induces can be corrected during OTE commissioning. However, as the telescope is operated and pointed at different positions within the field of regard, small temperature changes can occur at the level of tenths of a degree. These changes induce changes in the mirror figures, which must be controlled to maintain image quality.
During regular operations, NIRCam observations for WFS&C are executed every two days to monitor the Webb image quality. The weak lenses are used to image a bright target star using several defocus settings. The implied wavefront errors are corrected if they are deemed unacceptable, which is not expected to occur more frequently than every two weeks.
The software modules to analyze WFS data and control the mirror actuators are being developed by Ball Aerospace. The Institute is incorporating these modules into the WFS&C executive software, which handles the interfaces with other aspects of the Webb Science and Operations Center (such as the archive, proposal planning, and
flight operations). The entire WFS&C software subsystem (WSS) recently passed its critical design audit.The functionality of the WFS&C algorithms has been verified on the test bed telescope (TBT), a 1/6 scale
model of the Webb OTE, at Ball Aerospace. Additional verification and validation activities continue in the coming years. The NIRCam WFS&C hardware has recently been tested with good results in a cryogenic and vacuum environment (cryo-vac), using the NIRCam engineering test unit. Later tests include cryo-vac testing at Johnson Space Center of the integrated OTE and ISIM.
OPD maps inferred from WFS data are delivered to the Webb archive and are available to astronomers. Software that calculates PSFs, by combining OPD data with optics models and I&T data, is planned for development at the Institute. This is akin to Hubble’s TINYTIM software, but deals with the many optical complexities specific to Webb. Software with more limited functionality, called JWPSF, is already available at http://www.stsci.edu/jwst/software/jwpsf. This software produces calculations based on realizations of the wavefront error budget, rather than hardware characterizations. However, it is useful for prospective observers to assess the expected image quality as function of instrument, detector, wavelength, and filter.
Figure 2: The test bed telescope, a 1/6 scale model of the Webb optical telescope element at Ball Aerospace, was used to verify the functionality of the wavefront sensing and control algorithms developed for the Webb telescope.
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Webb Updatefrom page 35
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MIRI Status Scott Friedman, [email protected], and Gillian Wright, [email protected]
T he Mid-Infrared Instrument (MIRI) on the James Webb Space Telescope is highly versatile, offering imaging through nine
filters, four separate coronagraphs, low-resolution slit spectroscopy (LRS), and medium-resolution, integral-field-unit spectroscopy (MRS). Covering 5–28.3 microns, MIRI complements the other instruments on Webb, all of which operate at wavelengths shorter than about 5 microns.
Assembly and testing of MIRI is proceeding along several fronts. Through a collaboration among the ten countries of the nationally funded MIRI European Consortium (EC) and JPL, various pieces of the optics, mechanisms, structure, and detectors are being prepared and tested as the instrument gradually takes shape. The final instrument assembly, followed by a comprehensive thermal-vacuum performance test in a flight-representative environment, will take place at the Rutherford Appleton Laboratory (RAL) in England this year.
MIRI has a modular design and the subassemblies have endured a series of environmental tests, verifying performance at a range of temperatures, as well as acoustic, vibration, and lifetime tests, as appropriate. Each MIRI subassembly is then subject to a formal qualification review, and the majority of these reviews have already been held. Pre-ship reviews, held prior to delivery for integration at RAL, will verify that each subsystem meets its requirements, at least to the extent that it can be tested before assembly into the full instrument.
The mechanisms in an instrument are always of great interest because they must work in order to achieve full science performance. MIRI has four mechanisms: an imager filter-wheel assembly (FWA), two dichroic-grating-wheel assembles (DGAs), and a contamination control cover (CCC).
The FWA (Fig. 1) holds all imager filters, four narrow-band, coronagraphic filters and their associated Lyot stops, the double prism that disperses the light for the LRS, a neutral density filter, and an opaque blank. The FWA will be the most heavily used mechanism in the instrument.
The two DGAs hold dichroic beamsplitters and the twelve gratings used in the MRS. Obtaining complete spectral coverage over the full bandpass of the medium-resolution spectrometer requires three separate rotations of the DGAs. These mechanisms have recently been fully assembled and integrated into the MRS pre-optics assembly (Fig. 2). The FWA and the DGAs have completed flight-acceptance environmental qualification, and lifetime tests of these mechanisms are proceeding in parallel with flight instrument assembly.
The CCC (Fig. 3) acts as a front cover for MIRI. It is open when the observatory is launched and remains open for about one week to allow air to escape from the instrument. Then, as the instrument cools, the CCC is closed to keep contaminants from entering the instrument and freezing onto the optical surfaces. When Webb is sufficiently cold, the CCC
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Figure 1: The imager filter wheel. Toward the right side, in position 18, is the Lyot mask for the 10.65 micron coronagraph. Note the shape of the stops around each filter, which is designed to match the shape of the Webb primary mirror. (Photo courtesy of the MIRI European Consortium/CEA.)
Figure 2: The integration of the dichroic-grating assemblies (DGAs) into the spectrometer pre-optics. The red covers protect the delicate grating surfaces during integration. Three of the four image-slicer assemblies can be seen around the central location of the DGAs. (Photo courtesy of the MIRI European Consortium/UK-ATC/MPIA.)
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will be open for normal operations. However, during portions of coronagraphic target acquisition, it will be closed to prevent the bright target star from saturating the detector as it is placed in the center of a coronagraph. The CCC has completed all environmental and lifetime qualifications.
The focal-plane system consists of the focal-plane modules, which contain the detectors and the focal-plane electronics. MIRI has three 1024 × 1024, arsenic-doped silicon (Si:As) detectors, which differ from the detectors in all the other Webb instruments, due to the longer-wavelength
operating range. One detector is used for the imager, the coronagraphs, and the low-resolution spectrometer. The remaining two detectors are used for the medium-resolution spectrometer. Two different anti-reflection coatings are used to optimize the detector performance for short and long wavelengths. The flight, flight-spare, and engineering pathfinder detectors are shown in Figure 4. The detector performance is excellent, with demonstrated read noise of 14 electrons and dark current of approximately 0.1–0.2 electrons per second. The focal plane electronics are undergoing final design modifications as a result of thermal-vacuum testing. The modifications will ensure reliable communication of data to the rest of the Webb system. When modifications are complete, the focal-plane system will be delivered to the EC for integration into the instrument at RAL.
Because MIRI operates at longer wavelengths than the other instruments on the observatory, it must operate at a colder temperature. A cryocooler will maintain the detectors at 6.7 K and the MIRI instrument at below 10 K. The cooler has very complex interfaces across the whole of the Webb observatory. For that reason, it is being developed separately, and built up in stages that are integrated with the observatory construction. The MIRI optical system and complete MIRI cooler system will be tested together only at a late stage.
Detailed preparations are underway for the cryogenic performance test of the flight model. This test is expected
to begin in early 2011 and will last for 2–3 months. Upon successful completion of this test campaign, MIRI will be delivered to Goddard Space Flight Center for integration into the integrated science instrument module.
MIRI Statusfrom page 37
Figure 3: The MIRI contamination-control cover mounted on its ground mechanical support structure. The size of the cover is 109 × 126 mm. (Photo courtesy of the MIRI European Consortium/PSI-ETH Zurich.)
Figure 4: The MIRI flight and spare focal-plane modules. An anti-reflective coating, optimized for either short- or long-wavelength performance, has been applied to the surface of each detector, giving rise to their purple or blue appearance. (Photo courtesy of JPL.)
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Community Missions Office Alberto Conti, [email protected]
T he Institute has gained expertise from operating Hubble, building the Multimission Archive at Space Telescope (MAST) archive, and preparing for the science and mission operations of the James Webb Space Telescope. The Community Missions Office (CMO) is the focal point for bringing the benefits
of this experience to other missions and projects. In this role, CMO facilitates the Institute’s involvement in new initiatives and coordinates between mission teams and Institute personnel. It offers support for other missions in the areas of science operations, data curation and analysis, calls for proposals, peer reviews, grant administration, and education and outreach. In this way, CMO strives to adapt the Institute’s tools and services to the widest possible variety of space-science missions and ground-based observatories.
Recent CMO activities include:
KeplerCMO manages the Data Management Center (DMC) for
Kepler, a NASA mission searching for the signals of Earthlike planets transiting their host stars. The Institute built the DMC software before the Kepler launch in March 2009. The DMC performs the initial processing of Kepler data, performing a range of tasks from calibration to data retrieval and distribution to the user community. In collaboration with the Kepler Science Analysis Center at the NASA Ames Research Center, the DMC assembles the science data for release through the Kepler archive. Eventually, the Kepler archive and data products will be stored permanently in MAST.
MASTIn addition to overseeing MAST itself, CMO oversees
MAST’s education and public outreach project. This project is a coordinated effort with the Astrophysics Data System and the Infrared Processing and Analysis Center. The primary goal is to provide Hubble press release data in a form that is searchable, retrievable, and usable through MAST. The challenge is to capture the quality imagery from the press releases and to supplement it with ancillary data, so that the users can locate press releases by object, coordinate, or keyword. The imagery will then be retrievable through simple interfaces for use by educators, students, and the general public.
Virtual Astronomical Observatory (VAO)The VAO is designed to support an emerging change in the nature of astronomical research: access to
petabytes of data—1 PB = 1015 bytes—which demands new tools for analysis, comparison, and further discovery. The VAO is a multi-institution effort to standardize data and protocols for data exchange, and to build a robust foundation for the union of astronomical archives spread across the community. CMO manages the Institute’s contributions to the VAO, including maintenance of the VAO directory and support for the development of the program’s multi-year plan.
On-orbit servicingEarlier this year, NASA issued a Request for Information (RFI) entitled “The Feasibility of Using Human
Spaceflight (HSF) or Robotic Missions for Servicing Existing and Future Spacecraft,” soliciting input on how to improve our understanding of using the capabilities of NASA’s planned Constellation System, adaptations of the Constellation architectures, and/or robotic technologies to service a wide range of observatory-class spacecraft. In an effort coordinated by CMO, the Institute responded to this RFI jointly with the Johns Hopkins University and the Jet Propulsion Laboratory. The goal was to identify the scientific and technical benefits of servicing the Hubble, Webb, and future large ultraviolet-optical-infrared mission concepts, such as the Advanced Technology Large-Aperture Space Telescope (ATLAST; http://www.stsci.edu/institute/atlast/). The full text of the RFI response can be found at http://www.stsci.edu/institute/atlast/documents/ServicingRFI_stsci_jhu_jpl_final.pdf
If you want learn more about the Institute’s cumulative expertise and experience to support new missions for the science community, please visit http://cmo.stsci.edu.
Figure 1: A concept for a 16-meter, segmented-aperture space telescope, designed to cover a similar wavelength range to Hubble, but with 2000 times more sensitivity. Like Webb, this telescope would operate at the second Sun-Earth Lagrange point.
MAST, Multi-mission Archive at Space TelescopeAlberto Conti, [email protected]
T he Multimission Archive at Space Telescope (MAST) is NASA’s data repository for astronomy missions in the ultraviolet–optical wavelength range, including both active and legacy missions. MAST supports the astronomical community by facilitating access to its collections,
offering expert user support, and providing software for calibration and analysis.Currently, the volume of MAST’s holdings is about 113 terabytes (1 TB = 1012 bytes). Hubble data,
including the reprocessed data in the legacy archive, accounts for approximately 80% of the data. The Galaxy Evolution Explorer (GALEX ) is the source of nearly 15%. The remaining 5% consists of high-level science products (HLSPs) and data from other missions and observing programs, notably Kepler, Far Ultraviolet Spectroscopic Explorer (FUSE ), X-Ray Multi-Mirror Mission–Newton, and the Digital Sky Survey.
EPOCh Observations by the Deep Impact Spacecraft
MAST’s newest data source is a 2008 program of astronomical observations by the Deep Impact spacecraft, performed after its spectacular rendezvous with comet Tempel/P1 in 2005. Called “Extrasolar Planet Observations and Characterization” (EPOCh), this data includes new photometric time series for eight stars with transiting “super Jupiters.” The goal is to refine the physical properties of the giant planets, search for rings and moons that may orbit them, and search in these systems for smaller planets, down to the size of Earth.
The EPOCh data include images and spectra of the whole Earth from a distance, to help scientists anticipate future direct observations of extrasolar planets.
New Kepler Data and ServicesFour important Kepler catalogs—the original input
catalog, the subset of the input catalog that covers the Kepler field of view, the exoplanets catalog, and the catalog of Kepler observations—are now available from the MAST website (http://archive.stsci.edu/kepler/ ) and from standard Virtual Observatory catalog searches.
MAST’s publicly available Kepler data includes all the full-frame images and light curves for the planetary search program for the first and second mission quarters (Q0, Q1). The light curves for Q2 and Q3 are now available to Kepler guest observers and members of the science team.
Kepler HSLPs include the data for the first five planets discovered by Kepler, as announced by PI W. Borucki at the January 2010 meeting of the American Astronomical Society meeting (http://archive.stsci.edu/prepds/kepler_hlsp/ ).
GALEX General Release 6 The archive is ingesting the sixth general release (GR)
of GALEX data, which is from the medium imaging survey (MIS). It contains 3479 new GALEX tiles, or about 60% more sky area than the previous MIS delivery. The new tiles include co-added data from previously observed tiles, resulting in deeper coverage, and an object catalog in excess of 250 million sources. MAST plans on cross-matching all GALEX sources in this catalog with the Guide Star Catalog 2, the Two Micron All Sky Survey, and the Sloan Digital Sky Survey.
StarView on the Web In its first incarnation, StarView was a Java-based tool
for browsing astronomical data bases and analyzing data. At one time, it was the sole interface to the Hubble archive,
Figure 1: The eight “golden” full-frame images, obtained near the end of Kepler’s commissioning phase, can now be explored interactively. As an example, GALEX and Kepler public data are shown here.
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but that version of StarView has now been retired. Nevertheless, because it had a number of useful capabilities that the current web interface does not offer, we have created a web-based version: StarView (on thw web) 1.0. (http://starview.stsci.edu/web/ ).
The Hubble Legacy Archive The Hubble Legacy Archive (HLA; http://hla.stsci.edu/ ) now provides enhanced
images for all public science data from the Wide Field Planetary Camera 2 (WFPC2), Near Infrared Camera and Multi-Object Spectrometer (NICMOS), and Advanced Camera for Surveys (ACS) prior to the last servicing mission. It also provides images and spectra from the Space Telescope Imaging Spectrograph, spectra from the Faint Object Spectrograph and Goddard High Resolution Spectrograph, and extracted spectra from most of the NICMOS and a fraction of the ACS grism observations.
The HLA includes two categories of advanced data products: mosaics and HLSPs. Currently available for 67 pointings, mosaics combine ACS images of the same region of the sky obtained on multiple visits. Mosaics increase depth and widen sky coverage (http://hla.stsci.edu/hla_faq.html#mosaics). HLSPs are provided by independent science teams. Hubble HLSPs are based on fully processed—reduced, co-added, cosmic-ray cleaned, etc.—Hubble images and spectra, and all are ready for scientific analysis. These HLSPs represent the best that can currently be done with Hubble data.
High-Level Science Products:MAST currently holds a rich variety of HLSPs from Hubble and other missions, including surveys,
deep fields, and atlases (http://archive.stsci.edu/hlsp/ ). MAST is pleased to announce the availability of several new HLSPs:
ACS H-Alpha Survey of the Carina NebulaIn 2005, 43 orbits of Hubble observing time were spent studying the Carina Nebula in the light of
the Balmer-alpha line of hydrogen. Although these observations cover only a small, central part of the entire nebula, they produced one of the largest sets of contiguous ACS images ever collected. Most of the observations are part of a large mosaic, centered on the star clusters Trumpler 14 and Trumpler 16. M. Mutchler and his team have processed the data and created the mosaic images (http://archive.stsci.edu/prepds/carina/ ).
Archive of Nearby Galaxies: Reduce, Reuse, Recycle (ANGRRR))A team headed by J. Dalcanton, K. Gilbert, and B. Williams are producing an archive of stellar
photometry for non-Local Group galaxies within 5 Mpc of the Milky Way, based on primary and parallel, wide-filter, ultraviolet, and optical observations obtained by ACS and WFPC2. The first release of ANGRRR provides the results for galaxies within 3.5 Mpc (http://archive.stsci.edu/prepds/angrrr/ ).
Catalog of Cataclysmic Variables and Related ObjectsP. Godon and collaborators have created a catalog of FUSE spectra of cataclysmic variables (CVs)
and related objects. The catalog includes all CV types and sub-types, such as dwarf novae (U Gem, Z Cam, SS Cyg, WZ Sge, SU UMa sub-types), nova-like objects (VY Scl/anti-DN, UX UMa, SW Sex sub-types), and magnetic systems (IPs, Polars, DQ Her, AM Her sub-types). For each object, the catalog has at least one FUSE spectrum, basic data about the system including figures and tables, and possibly a fitted theoretical spectrum—in cases where the continuum can be modeled successfully. The catalog also includes various objects related to CVs, such as novae of all types, symbiotic stars, and some pre-CVs (http://archive.stsci.edu/prepds/cvaro).
Dusty Interacting Galaxy GADGET-SUNRISE Simulations (DIGGSS)DIGGSS is a database of simulated galaxy merger images and associated data products. These
simulations were created and analyzed with the support of HST Theory Programs 9515, 10678 (PI Joel Primack), 10958, and 11759 (PI Patrik Jonsson). The N-body/SPH code GADGET produced the simulations, which were processed through the Monte-Carlo radiative transfer code SUNRISE to produce mock SDSS–g-band images at 11 different viewing angles. The effects of dust and new star-formation are included (http://archive.stsci.edu/prepds/diggss/ ).
The Far-UV Spectral Atlas of B StarsM. Smith has published a far-ultraviolet spectral atlas of ten sharp-lined B0–B9 stars near the main
sequence. The atlas is based primarily on reprocessed FUSE data, but includes data from Copernicus, IUE, and Hubble. The atlas provides tables of all recognizable photospheric and interstellar-medium lines in the spectra of the B0, B2, and B8 stars—some 2000 lines in each case. These tables should enable astronomers to synthesize B-star spectra (http://archive.stsci.edu/prepds/fuvbstars/ ).
Figure 2: Sample ACS GRISM spectrum. Preview of the extracted GRISM spectrum of a z = 2.82 BAL QSO (an X-ray source identified in the Chandra Deep Field South) included in the DR3 data. The preview includes a plot of the spectrum, a direct image, and a cutout of the two-dimensional GRISM data. A similar preview is available for each extracted target.
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FUSE Survey of Cataclysmic VariablesC. Froning has provided the FUSE Survey of Cataclysmic Variables, which contains 178 FUSE
observations of 99 CVs (http://archive.stsci.edu/prepds/fuse_cv/ ).
GOODS NICMOS Archival DataAs a part of a Hubble archival research proposal titled “Probing the Galaxy Population at z ~ 7–10
Using Archival ACS & NICMOS Data,” PI R. Bouwens and colleagues retrieved and processed nearly all NICMOS camera 3 F110W and F160W data taken over the GOODS north and south fields (http://archive.stsci.edu/prepds/goodsnic/ ).
STIS Next Generation Spectral Library (NGSL Version 2) S. Heap and D. Lindler have delivered STIS spectra of 374 stars. Each includes segments from
gratings G230LB, G430L, and G750L merged into a single spectrum covering ~2000–10,000 Å (http://archive.stsci.edu/prepds/stisngsl/ ).
Hubble Fellowship NewsRon Allen, [email protected]
The Hubble Fellowship Program provides postdoctoral fellowships to candidates of exceptional research promise. The program includes the scientific goals addressed by any of the missions in NASA’s Cosmic Origins Program. These missions presently include: the Hubble Space
Telescope, Spitzer Space Telescope, Stratospheric Observatory for Infrared Astronomy, the Herschel Space Observatory, and the James Webb Space Telescope. This program is funded by NASA and is open to applicants of any nationality. The fellowships are tenable at U.S. host institutions of the fellows’ choice, subject to a maximum of one new fellow per host institution per year. The duration of the fellowship is up to three years. More details are available at the Fellowship web site (http://www.stsci.edu/institute/org/spd/hubble-fellowship).
2010 Hubble Fellows SymposiumThis year marked the 20th anniversary of the founding of the Hubble Fellowship Program. In honor of
that milestone, all past Hubble Fellows were invited to attend the annual Hubble Fellows Symposium. This symposium was held at the Institute on March 8–11, 2010. The presentations by current Fellows were rounded out with contributions from past Fellows and NASA staff. A particular highlight was a talk by Prof. Riccardo Giacconi on the genesis of the Hubble Fellowship Program, reproduced below. (The original program focused on research and researchers associated solely with the Hubble Space Telescope.)
Figure 3: A section of ACS Mosaic 597, consisting of eight visits on galaxy cluster CL0152–1357. The color image is a composite of data in F625W, F775W, and F850LP, for a total of 57200 s in eight visits, laid out in a 2×2 grid.
MASTfrom page 41
The program and recorded video of the symposium are available at this archive site (https://webcast.stsci.edu/webcast/archive.xhtml).
Selection of the 2010 Hubble FellowsThe 2010 Hubble Fellow Selection Committee met at the Institute on January 11–12 to consider
the 236 applications that were received by the deadline of November 5, 2009. The selection criteria remained the same as in the past. The number of Hubble Fellowships to be awarded for 2010 remained at 17. The 15-member committee was chaired by Prof. Marc Pinsonneault (Ohio State University). Offers were made, and by mid-February the list of 2010 Hubble Fellows was complete; see Table 1. They will take up their new fellowships in the fall of 2010.
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Figure 1: Participants in the 2010 Hubble Fellows Symposium, including fellows who were appointed in 2007, 2008, and 2009, a number of former Hubble Fellows, the Giacconi Fellows currently at the Institute, the present and two past Institute directors, and the present and past Hubble Fellows Program directors.
Figure 3: Prof. Chris McKee at the 2010 Hubble Fellows Symposium.
Figure 2: Prof. Giacconi addresses the 2010 Hubble Fellows Symposium at the Institute on the genesis of the Hubble Fellowship Program.
2010 Hubble Fellow PhD Institution & Yr Host InstitutionJoshua Carter MIT, 8/09 SAOCaitlin Casey U Cambridge, 9/10 IfA/UHIMichael Cooper UC Berkeley, 5/07 UC IrvineSelma de Mink Utrecht U, 4/10 STScITrent Dupuy U Hawaii, 5/10 SAODaniel Fabrycky Princeton U, 8/07 UC Santa CruzKaroline Gilbert UC Santa Cruz, 6/08 U WashingtonHenry Hsieh U Hawaii, 4/07 IfA/UHIRyan Keisler U Chicago, 8/10 U ChicagoDusan Keres U Massachusetts, 5/07 UC BerkeleyMaryam Modjaz Harvard U, 6/07 Columbia UPascal Oesch ETH Zurich, 8/10 UC Santa CruzRyan Quadri Yale U, 12/07 OCIWBeth Reid Princeton U, 9/08 LBNLHilke Schlichting Caltech, 5/09 UCLADebora Sijacki MPIA and LMU, 9/07 Harvard College ObsMatthew Walker U Michigan, 8/07 Harvard College Obs
2010 Hubble Fellows
Hubble Fellows, the Future is in Your HandsRiccardo Giacconi
T he creation of the Hubble Fellows Program was part of our (the scientific staff and I) vision of what the Institute was designed to accomplish. The Hornig Committee had recommended that an independent institute should be created to ensure the broadest participation by the
scientific community in the Hubble program, and we also had the funny notion that the purpose of building Hubble had to do with the study of our Universe. For this reason we had developed a methodology which we called a science systems engineering approach to guide us in developing the necessary hardware and software tools to carry out our operations from end to end. This meant that we examined all required intermediate steps from proposal selection support to the archiving of calibrated data to determine that each step was properly conceived and ready to perform as required. It was natural to extend this systems approach to include the question of whether the community had the required number of scientists to effectively use the data, and the assistance and computer support appropriate for the task.
We were approaching a period in optical astronomy in which the capital investment in facilities was to increase by factors of about 100. Up to that point, university or institutional funds had provided the bulk of the support required to carry out most of the research in astronomy through salaries and internal research funds. This support had been essential to supplement the meager funds provided by NSF and NASA. Given the magnitude of the program that was envisaged with Hubble, however, it was no longer possible for research institutions to provide the scale of support necessary to make full scientific use of the data. While NASA would directly provide the funding for the builders of the scientific instruments to analyze their own data for a few years, most of Hubble’s observing time (>70%) would be used by astronomers who had not had a direct previous association with the Hubble project.
The Institute initiated a study led by professor Neta Bahcall (then a staff member) of what the Institute would need to provide (ultimately by NASA) to ensure the proper utilization of the data within a reasonable time. The committee recommended that the Institute make grant funds available to the competitive winners of observing time.
Yet I felt that something more was required. I was troubled to see PI groups use postdocs in essence as research assistants, without much opportunity for the pursuit of their own research, and I was fearful that this would become the norm in the future.
I remembered a suggestion for a different approach that Chris McKee had made to me while we were strolling in the English Gardens in Munich where we were attending a meeting in 1982. If I remember correctly (Chris is here today and can correct me), I was complaining about theoreticians who, in my opinion, tended to look down on observers and experimentalists as mechanics rather than natural scientists. In particular, I was upset by the fact that theoreticians who had no management capabilities and little physical intuition about the natural world always chaired the National Academy of Sciences (NAS) Decadal Surveys. While thus pleasantly engaged in this debate, he dropped his suggestion of creating fellowships for research.
Thinking about it later, the idea struck me as a real way to go. The Institute would be able to create a means to support free research and pursuit of excellence while making a statement against conformism and mediocrity, which as usual seemed to abound. We would select the best young astronomers, applying from anywhere in the world, willing to work in the U.S., and interested in fields broadly related to the Hubble program (now the Hubble Fellowship includes Herschel, HST, JWST, Sofia, and Spitzer ). Their work would occur in a U.S. institution which was interested in the research and willing to provide the overhead support required. To my mind this not only took care of administrative and technical support for the Fellows, but also gave the Fellows a temporary home (with seminars and colleagues), and possibly some direct mentorship. The Fellows could transfer during their fellowship from one institution to another, under the same conditions. The only restriction was that no more than two Hubble Fellows could reside at the same institution at the same time. The salary offered the Fellows would be competitive and the initial appointment for two years could be extended for a third one. In addition to salaries and benefits, the Fellows would receive a small budget for research and travel. No duties were imposed on the Fellows except to meet once a year at the Institute for a symposium in which each of them would give a seminar on their research. These rather liberal rules were inspired by the conviction that an atmosphere of freedom was most conducive to creativity.
The entire program to support research done with Hubble was very well received by Dr. Charlie Pellerin, then director of the NASA Astrophysics Division, and was successfully implemented by the Institute for the last 20 years. It has been adopted by other NASA observatories, including Chandra
Text of a talk given at the Institute on March 8, 2010, by Riccardo Giacconi on the occasion of the 20th anniversary of the start of the Hubble Fellowship Program.
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and Spitzer, and the program was so successful that NASA ended up providing more grant funding for astronomy than NSF, the agency that had traditionally supported ground-based astronomical research. The program was brilliantly executed under the guidance of the successive heads of Academic Affairs at the Institute, which included Len Cowie, George Miley, Colin Norman, Nino Panagia, and Ron Allen.
Has the program worked? It may be too early to judge, although the general feeling in the community is positive. I have discussed with Matt Mountain and Ron Allen how we can go about evaluating its effects in the future. It is difficult to come to easy conclusions because of the different points of view involved and the fact that assessment will have to continue for a while; for now Ron Allen has shown me some figures he has collected which are very interesting.
(1) Has the program been good for NASA? It would appear so, given the many publications and credits. (2) Has it been good for the host institutions? We do not really know and we should find out. (3) Has it been good for the Fellows? Here it would seem that the answer is already a clear yes. Out of about 200 Fellows in the first two decades of the program, some 95% have now a permanent science-related position, mostly in academic and research institutions. (4) Has it been good for astronomy? It will take time to get a clear picture of the scientific productivity of the Hubble Fellows and of the quantity and quality of their work as compared to that of all astronomers in their age group. An interesting piece of data has been the finding that the participation of Hubble Fellows in the current NAS 2010 Decadal Survey committees seems to be quite large, as compared to that of other participants in the same age group. Thus, the impression is that the community has a high opinion of the Hubble Fellows. This also means that the Hubble Fellows will have increasingly more to say about the future of astronomy in the U.S. This is not only an honor, but also a great responsibility.
I will conclude my remarks on the theme of the Fellows’ responsibility. I start with a little detour: since the time of the Greek golden age, and later since the Renaissance, artists have asserted their individuality by signing their work. This drive to individual freedom of expression has taken us to the point that some artists today feel they have an innate right to be supported by society to carry out their creative impulses. (Actual experiments of state support for artists have generally been rather dismal). Many scientists today also feel the same way, most notably in Italy and France, but also here in the U.S. I do not think we have an innate right to be supported and believe instead that all scientists should earn their living by working on things useful to the community. These can be teaching, building or operating facilities, outreach activities, etcetera. All should be allowed and encouraged to pursue free research of their choosing for half their time at work and of course as much as they wish and can on their own time. We might recall that Einstein was working at the Swiss patent office in the years preceding 1905. I think Hubble Fellows have a special responsibility, having been given the privileges accorded to the best and the brightest, and that responsibility is to lead. That duty is particularly important today, when rationality is seen as elitist and when research, particularly in the physical sciences, is under some threat. My belief is that scientists must take the future in their own hands and help in improving our programs, our institutions, our academies, and also our funding agencies. How you will respond to this tall order is important to all of us, because it is in your hands to continue and expand our scientific heritage.
"I think Hubble Fellows have a special responsibility, having been given the privileges accorded to the best and the brightest, and that responsibility is to lead."
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May Symposium 2010Jason Kalirai, [email protected] and Massimo Robberto, [email protected]
T he 2010 May Symposium, “Stellar Populations in the Cosmological Context,” took place at the Institute on May 3–6, and attracted nearly 200 participants. The topic of the symposium was inspired by the enormous progress over the last two decades in two areas: the detailed
study of nearby, resolved stellar populations, and the discovery and the characterization of high-redshift galaxies. Furthermore, the new panchromatic capabilities of Hubble’s Wide Field Camera 3 (WFC3) are now enabling a new leap forward in exciting research related to stellar populations across a diverse range of redshifts. Therefore, the premise of the symposium was that the physical processes and observed characteristics of local stellar populations, observed in a variety of environments, will become a fundamental tool for elucidating the formation, structure, and evolution of galaxies at all cosmic times and distances.
The symposium was a mix of 40 invited and contributed presentations, and 50 shorter presentations, where participants presenting posters were given an opportunity to advertise their work. Over 25% of all time during the meeting was reserved for extended discussions, including summaries at the end of each day led by various members of the scientific organizing committee. The symposium also included a special public talk one evening by astronaut Dr. John Grunsfeld (now the Institute’s Deputy Director) entitled “Hugging Hubble.” The banquet was held at the Maryland Science Center and included a screening of the new “Hubble 3D” IMAX movie.
The symposium started with a review of the latest observational and theoretical findings on the formation of stars and stellar populations. While star formation appears to be ubiquitous in the universe, the process is surprisingly inefficient. A variety of mechanisms (i.e., magnetic fields, turbulence, feedback) have been
invoked to explain the high gas/star-mass ratio typically observed in star-forming regions. No one mechanism seems to be dominant, and indeed all may be relevant in certain environments or star-formation phases.
Observations of systems like 30 Doradus, in the Large Magellanic Cloud (LMC), provide strong evidence for star formation triggered by early generations of massive stars. The presence of massive stars is also often invoked for opposite cases, where molecular clouds have been disrupted and star formation therefore prevented. The timescale for massive stars to disrupt the parental cloud is apparently a critical factor for the evolution of star clusters. At the other end of the mass spectrum,
new WFC3 observations of low-mass, pre-main-sequence stars in the LMC suggest that they continue to accrete for long timescales, thereby also providing an important tracer of the recent star formation.
Both individual stars and stars in clusters display simple initial mass functions (IMFs), with intriguing similarities in their power-law indices. While there are indirect indications of abnormal IMFs in some galaxies, there is no compelling evidence against a universal IMF in places where individual stars can be resolved and counted. The survival of clusters as bound systems may determine their currently observed mass distributions.
In globular clusters like Omega Cen and NGC 2808, an even more complex interplay between stars and gas, including feedback from the first evolved stars, has been invoked to explain the presence of multiple populations with different helium abundances. For over a century now, these systems have been treated as simple stellar populations that formed at the same time and that have the same chemical composition.
Figure 1: Poster for the 2010 May Symposium
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Therefore these results have the potential to shatter our understanding of cluster formation and evolution. It remains to be explored whether the presence of multiple populations in clusters is the rule or the exception.
There are many nearby stars older than 10 Gyr, which must have formed at redshifts greater than two. (No genuine “first star”—Population ΙΙΙ—has yet been found.) With iron abundances as low as [Fe/H] ~ –5, we can study the metallicities of these old stars in detail, and may discover important clues on the IMF in the early universe. For example, the high enhancement in alpha-elements of the lowest metallicity stars in the halo and dwarf galaxies provides strong evidence of enrichment from core-collapse supernovae.
Ultra-sensitive, wide-area imaging and spectroscopic observations have revealed abundant substructures in the halo of the Milky Way halo, as well as in the halos of other nearby galaxies, such as M31, M33, and NGC 891. These substructures, such as the Sagittarius stream, represent spectacular fossil records of past galaxy mergers and encounters, often traceable for hundreds of kiloparsecs. The overall structure of galaxies like the Milky Way—halo, bulge, and disk component—can be shaped by the merger history. It is an open question how closely such galactic cannibalism is linked to the shape and structure of galactic halos of dark matter. As rapidly as the observations are characterizing these substructures in nearby galaxies, new high-resolution computer simulations of galactic assembly are providing testable predictions in the cosmological context.
The knowledge gained from high-resolution studies of the kinematics, abundances, ages, and morphologies of various stellar populations in nearby clusters and galaxies is dramatically advancing our models of the evolution of stars. As galaxies are collections of stars themselves, the uncertainties in these models are necessarily passed along to studies that attempt to interpret the integrated light from distant galaxies using population synthesis techniques. This connection—moving from studies of detailed resolved stars to unresolved light—lies at the heart of many astrophysical topics under the rubric of galaxy formation and evolution. An example is provided by state-of-the-art Hubble imaging surveys that combine existing optical data from the Advanced Camera for Surveys with new, ultra-sensitive, high-resolution ultraviolet and infrared imaging from WFC3. Such surveys have discovered over a hundred galaxies at a redshift greater than seven, when the universe was only a few hundred million years old. Preliminary estimates of the masses, ages, and star-formation histories of these systems can be calculated by fitting the spectral energy distributions of these objects, using the theoretical models derived from local populations. Another example is provided by the study of galaxies at intermediate redshifts, when the cosmic star formation rate peaks. For these systems, the infrared grism of WFC3 is greatly improving our detailed knowledge of the stellar makeup of galaxies.
Despite the enormous progress that has been made on the study of stellar populations across cosmic time, some of the uncertainties in the fundamental properties such as age, metallicity, and mass remain large. New data sets can help remove degeneracies in modeling the light from these sources. Specifically, in the future, the James Webb Space Telescope and its infrared sensitivity will complement the current studies and push this science to the next level.
The web page for the 2010 May Symposium is http://www.stsci.edu/institute/conference/spring2010. Included on the web page is a 100-page document with the “take home” message from each of the symposium presenters (under the “Conference Summaries” link). All of the May Symposium presentations have been webcast and are archived along with .ppt or .pdf presentations at this web site: https://webcast.stsci.edu/webcast/index.xhtml
Figure 2: NGC 5907 is an edge-on spiral galaxy similar to the Milky Way. In this ground-based image, presented by May Symposium participant David Martinez-Delgado, an extended tidal stream can be seen wrapping around the galaxy. This picture highlights galactic cannibalism whereby the stellar populations of a low-mass satellite are shredded off and accreted into the potential of a massive galaxy, forming a complex of arcing loops. (Martinez-Delgado, D., et al. 2008, Astrophysical Journal, 689, 184)
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Hubble Science Year in ReviewAnn Jenkins, [email protected]
C ommunicating the wonder of exploration and the excitement of discovery are goals of the Hubble Space Telescope Science Year in Review. Thousands of papers have been written on Hubble results, but the Science Year in Review distills the top annual discoveries into
laymen’s terms—complete with full-color, top-flight graphics and illustrations, and a multitude of amazing Hubble images. The annual publication shares the story and science of Hubble to engage the public in the telescope’s spectacular success.
Begun in 2004, the Science Year in Review is the flagship annual publication on Hubble results, but it is also much more. The book features an updated history of the telescope, a discussion of the design and current instrument configuration, a section on how operations are conducted, a series of profiles on Hubble team members, and a full-color poster. The upcoming volume—the 2009 edition—also describes the challenges of Servicing Mission 4 and showcases the early release observations.
The book is distributed free of charge to libraries, research institutions, and members of the science-attentive public. It is produced by a small cadre of people at the Institute and Goddard Space Flight Center who research, write, illustrate, design, and edit it.
The majority of the book involves interviewing astronomers about their cutting-edge research, then distilling that information into words and concepts that can be understood by the average citizen. The Profiles section is also the product of interviews of a cross-section of Hubble teammates with a goal of painting each one as a complete person and showing their diverse talents and interests outside of the workplace.
Each year, the book’s “Operating Hubble” section follows a specific, large, and important observation, explaining how the campaign was planned and executed. For 2009, this observation was the Hubble Ultra Deep Field IR, the infrared counterpart to the deepest-ever visible-light image, the Hubble Ultra Deep Field in 2004. The new observation—which used the near-infrared capability of Hubble’s newly installed Wide Field Camera 3—penetrates even more deeply into the same section of sky to see even more distant galaxies.
The science articles for the 2009 book run the gamut: from an asteroid’s collision with Jupiter and a journey to the heart of the Milky Way Galaxy, to narrowing the possible explanations for dark energy—and nearly everything in between.
An effort is currently underway to place all of the editions of the Science Year in Review on line. As of now, only 2006, 2007, and (soon) 2008 are on line, but eventually, the full complement will be available. The user is given the option of downloading a pdf of each complete volume, or of downloading just a single chapter or section. The on-line versions are compliant with the Americans with Disabilities Act, which means each document can be read by a screen-reading machine for the sight-impaired.
To view the on-line editions of the Science Year in Review, please go to http://hubblesite.org/hubble_discoveries/science_year_in_review/
In chronicling the story of Hubble and its history of discovery, the Science Year in Review series keeps the public regularly apprised on Hubble’s robust program of exploration. A wonderful addition to any science library, this book is a tribute to the many people who make the Hubble mission possible.
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Magnetic Filaments in an Active GalaxyAndy Fabian
NGC 1275 is located about 235 million light-years away in the constellation Perseus. Also known as Perseus A, the galaxy lies at the heart of the Perseus cluster, a rich collection of more than 500 galaxies. The largest galaxy in the cluster, NGC 1275 is also one of the closest giant elliptical galaxies.
The galaxy is home to a supermassive black hole that is accreting material at a very rapid rate. The presence of this central black hole makes the giant galaxy a well-known radio source and a strong emit-ter of x-rays. NGC 1275 is classified as an active galaxy—one that shows physical activity near its core and radiates at higher-than-average luminosity levels over some or all of the electromagnetic spectrum. Gas, swirling near its black hole, is causing energetic activity that creates spherically-shaped “bubbles” of material to be ejected into the surrounding galaxy cluster. Extremely long filaments of cold gas are seen emanating from the core of the galaxy and extending out in the wake of the rising “bubbles.”
These gossamer-appearing filaments have withstood the hostile, high-energy environ-ment of the galaxy cluster for more than 100 million years. The gravitational forces alone within NGC 1275 would destroy the filaments within 10 million years if not for additional forces keeping them in equilibrium. The fila-ments are also likely experiencing turbulence from the rising, hot “bubbles.”
Indeed, the long, gaseous tentacles stretch out beyond the galaxy into the multimillion degree, x-ray–emitting gas that fills the cluster. The tentacles provide evidence in visible light of the intricate relationship between the central black hole and the surrounding gas in the gal-axy cluster. But why have they not heated up, dispersed, and evaporated by now, or simply collapsed under their own gravity?
Using Hubble data, a team of astronomers led by Andy Fabian from the University of Cambridge, UK, has proposed a solution—magnetic fields hold the charged gas in place and resist the forces that would distort their filamentary structure. The team deduced this by resolving, for the first time, the individual threads of ionized gas that make up the fila-ments. The team found that the tentacles are only about 200 light-years wide, are often very straight, and extend for up to 20,000 light-years. Such thin filaments require con-straining magnetic fields for integrity and survival. The magnetic field lines provide a skeleton that holds the filaments together against their surrounding forces.
The thinner the filament, the stronger the maintaining magnetic field must be. Hubble data enabled the team to measure individual filaments and deduce the strength of the magnetic fields that are in equilibrium with the hot gas. The astronomers determined that the strength of the fields are only about 1/10,000th that of Earth’s, but because they extend over galaxy-sized regions, they contain an immense amount of magnetic energy.
This edition of the Institute Newsletter continues to reprint science articles from NASA's annual Hubble 200X Science Year in Review. We are pleased to continue this service with "Magnetic Filaments in an Active Galaxy" by Andy Fabian and "Dark Matter and Galaxy Life in a Supercluster" by Dr. Meghan Gray and Dr. Catherine Heymans, from Hubble 2008."
Fine, thread-like filamentary structures surround active galaxy NGC 1275. The red fila-ments are composed of cool gas suspended by a magnetic field, and are enveloped by the 100-million-degree Fahrenheit hot gas in the center of the Perseus galaxy cluster.
Continuedpage 50
The team also found the amount of gas contained in a typical thread is around one million times the mass of our own Sun. The gas forming them is also roughly the same mix of hydrogen, helium, and other elements that comprise the Sun.
Most ionized gases possess magnetic fields. Churning gas can wind up the fields, making them stronger. The black hole, while not the source of the magnetic field, causes motions that stir up the gas and amplify the fields.
The filamentary system in NGC 1275 provides a striking visual example of the workings of extragalactic magnetic fields. These structures may be common on much smaller scales in normal galaxies. In our
own Milky Way galaxy, there is an arc-like feature near the central black hole that is believed to be hot plasma flowing along magnetic field lines.
Immense networks of filaments similar to those in NGC 1275 are found around many other, more remote central cluster galaxies, but they cannot yet be observed with comparable resolution. For now, the team will apply their understanding of NGC 1275 to interpret observations of these more distant galaxies.
Further ReadingCanning, R.E.A., et al., "Star Formation
in the Outer Filaments of NGC 1275," Monthly Notices of the Royal Astronomical Society, 405, 115–128, 2010.
Conselice, C.J., J.S. Gallagher III, and R.F.G. Wyse, “On the Nature of the NGC 1275 System,” Astronomical Journal, 122, 2281–2300, 2001.
Fabian, A., R. Johnstone, J. Sanders, et al., “Magnetic Support of the Optical Emission Line Filaments in NGC 1275,” Nature, 454, 968–970, 2008.
Hatch, N.A., C. Crawford, and A. Fabian, “Detections of Molecular Hydrogen in the Outer Filaments of NGC1275,” Monthly Notices of the Royal Astronomical Society, 358, 765–773, 2005.
Kent, S.M., and W.L.W. Sargent, “Ionization and Excitation Mechanisms in the Filaments Around NGC 1275,” Astrophysical Journal, 230, 667–680, 1979.
Salome, P., “Cold Gas in the Perseus Cluster Core: Excitation of Molecular Gas in Filaments,” Astronomy & Astrophysics, 484, 317–325, 2008.As illustrated in these Chandra and Hubble images, gas swirls near NGC 1275’s
black hole, creating energetic activity that ejects “bubbles” of material into the surrounding galaxy cluster. Immensely long filaments form when cold gas from the galaxy’s core is dragged out in the wake of the rising “bubbles.”
One of the United Kingdom’s foremost high-energy astrophysicists, Andy Fabian has built his career by us-ing the techniques of x-ray astronomy to investigate extreme astrophysical conditions. His interest in space astronomy dates to his childhood in the U.K. He completed his undergraduate work in physics at King’s College, London, and earned his Ph.D. from the Mullard Space Science Laboratory at the University College London. Dr. Fabian is a Royal Society Professor at the Institute of Astronomy at the University of Cambridge and President of the Royal Astronomical Society. His research interests are in accreting black holes and clusters of galaxies.
Magnetic Filamentsfrom page 49
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Dark Matter and Galaxy Life in a SuperclusterDr. Meghan Gray and Dr. Catherine Heymans
Like lights strung on a Christmas tree, galaxies in the massive supercluster Abell 901/902 appear to hang on mysterious, invisible branches. Mathematical models describing the origin of hydrogen, helium, and other light elements during the birth of the universe, or “Big Bang,” predict that ordinary matter—the protons and neutrons that make up the stars, planets, gas, dust, and us—accounts for only a small frac-tion of the universe. The bigger fraction consists of some unknown material—dubbed “dark matter” by scientists—which does not emit any radiation that can be detected by conventional methods, but whose gravitational influence directs and constrains the formation of the large-scale structures of the universe (see sidebar on page 53). Recent Hubble observations of Abell 901/902 have helped to “illuminate” this invisible dark matter and the large cosmic “web” in which it entangles “normal” matter.
The Search for Dark MatterAstronomers, using Hubble’s
Advanced Camera for Surveys, have produced a detailed map of the dark matter framework in Abell 901/902, and of the hundreds of individual galaxies that trace it. The map was constructed by observing the light from more than 60,000 distant, background galaxies that are far beyond the supercluster. To reach Earth, the light from these faraway galaxies traveled through the dark matter surrounding the closer supercluster. As it did so, the light was bent by the dark mat-ter’s massive gravitational field—a phenomenon known as “gravita-tional lensing.” Astronomers used this observed, subtle distortion of the background galaxies’ shapes to compute the amount of dark matter in the light’s path and then to reconstruct the dark matter dis-tribution in the supercluster.
Gravitational lensing, a direct prediction of Albert Einstein’s 1916 Theory of General Relativity, comes in two forms: strong and weak. Strong lensing dramatically bends the light from distant galaxies into arc-like shapes. Weak lensing dis-torts the images to a much lesser degree. Einstein realized that these small distortions could not be seen from the ground given the technol-ogy of his day, and so left this aspect of his theory to be validated by future experimentalists. Now, 93 years later, Hubble and the newer class of astronomical instruments have sufficient angular resolution to record even the perturbations of weak lensing. In this case, Hubble data were used to analyze large numbers of galaxies to find consistent, small, gravity-produced distortions.
Continuedpage 52
As predicted by Albert Einstein’s General Theory of Relativity, a gravitational lens is formed when the light from a very distant, bright source is bent around a massive object (such as a cluster of galaxies) between the source object and the observer. With strong lensing, there are easily vis-ible distortions such as the formation of rings, arcs, and multiple images. With weak lensing, the distortions of background sources are much smaller and can only be detected by analyzing large numbers of sources. The bowtie-shaped distortion illustrated in the weak lensing case above is an exaggerated example of what would actually be seen. Researchers Gray and Heymans used weak lensing, employing the subtle distortion of the galaxies’ perceived shapes to reconstruct the distribution of intervening mass along Hubble’s line of sight.
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Astronomers identified four main areas in the supercluster where dark matter has collected into dense clumps. These total 100 trillion times the Sun’s mass. The areas are also the location of hundreds of old galaxies that lived through a violent history during their travels from the edges of the superclus-ter into the denser central region.
The dark matter map is 2.5 times sharp-er than a previous ground-based survey of the supercluster and shows details and nuances not possible with ground-based telescopes, whose images are further distorted by Earth’s atmosphere, thereby complicating the analysis. This marks the first time that irregular clumps of dark matter have been detected and cataloged in Abell 901/902.
Galaxy DetailsMapping the underlying dark matter in
the supercluster was just one use for the Hubble data, however. Astronomers also studied in detail the galaxies themselves to understand how galaxies are influenced by the environment in which they live.
As the universe evolves, galaxies are continually drawn into larger and larger groups, clusters, and superclusters by
Dark Matterfrom page 51
A composite image of galaxy cluster Abell 901/902 taken with Hub-ble and the MPG/ESO 2.2-meter telescope in Chile. The magenta-tinged clumps indicate the location of dark matter as derived through analysis of an effect called “gravitational lensing,” which slightly dis-torts the galaxies’ shapes.
The Hubble study revealed the distribution of dark matter in the supercluster Abell 901/902, composed of hundreds of galaxies. The magenta-tinted clumps represent a map of the dark matter in the cluster, and the supercluster galaxies lie within the clumps of dark matter. The four flank-ing images are details of the central images. Astronomers assembled these photos by combining a visible-light image of the supercluster taken with the MPG/ESO 2.2-meter telescope in La Silla, Chile, with a dark matter map derived from observations with the Hubble Space Telescope.
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Continuedpage 54
the pull of gravity. On the fringes of a supercluster, galaxies are still traveling relatively slowly and feel-ing the first effects of the cluster environment. Galaxies located in this relative isolation appear very different from those found in the most crowded regions of a super-cluster. Galaxies in the center of the supercluster are generally rounder, tending to be elliptical rather than spiral. They also tend to be full of old, red stars rather than still forming hot, young blue stars. The researchers believe environ-ment plays a large role in this difference.
The Hubble survey data revealed that more collisions occur between galaxies in the regions toward which the galaxies are traveling than in the centers of the clusters. By the time the galaxies reach the cluster’s center, they are mov-ing too fast and with too much momentum to collide and merge. On the way to or from the clus-ter’s periphery, however, they move more slowly and have more time to interact.
The Challenge Ahead This study of dark matter and
galaxies was part of the Space Telescope Abell 901/902 Galaxy Evolution Survey (STAGES), led by Meghan Gray of the University of Nottingham and Catherine Heymans of the University of Edinburgh, both in the United Kingdom. STAGES spanned one of the largest sections of sky ever observed by Hubble, an area requiring 80 Hubble imag-es to cover the entire field. Abell 901/902 is located 2.6 billion light-years from Earth and is more than 16 million light-years across.
Having mapped the densest regions of dark matter in this supercluster, the STAGES team now wants to use Hubble to understand even more about this elusive substance. Even though they have made a very high resolution, detailed map, more data are required to see lower-mass filaments that they believe link together the dark matter structures and form the giant cosmic “tree.” With new data, they also seek a more detailed understanding of how galaxies form, evolve, and interact with each other during their lifetimes within the supercluster environment.
Further ReadingFreeman, K., In Search of Dark Matter, New York, NY: Praxis Publishing Ltd., 2006.Heymans, C., et al., “The Dark Matter Environment of the Abell 901/902 Supercluster: A Weak Lensing
Analysis of the HST STAGES Survey,” Monthly Notices of the Royal Astronomical Society, 385, 1431–1442, 2008.Massey, R., et al., “Dark Matter Maps Reveal Cosmic Scaffolding,” Nature, 445, 286–290, 2007.Refregier, A., “Weak Gravitational Lensing by Large-scale Structure,” Annual Review of Astronomy and
Astrophysics, 41, 645–668, 2003.
Dark Matter and the Cosmic WebDark matter is an exotic, invisible form of matter that accounts for most of the universe’s mass. This mysterious
matter can only be detected by its gravitational pull. It should not be confused with dark energy, a repulsive force (whose origin is currently unknown) opposing the force of gravity. Studying dark matter may eventually unlock the secret to dark energy, which influences how dark matter condenses.
In this artistic depiction of the cosmic web—the large-scale structure of the universe—each bright knot is an entire galaxy, while the purple filaments show where dark matter exists between the galaxies. The cosmic web is believed to be the skeleton of the universe. This web of dark matter formed in the very early universe because of extremely small-scale fluctuations in the density shortly after the Big Bang. The very rapid inflationary growth, which the universe underwent shortly after the Big Bang, grew these tiny fluctuations into the large-scale web-like structure we see today.
Normal matter is gravitationally attracted to the strands and clumps in the dark matter web. Its resulting contraction gives rise to the formation of stars and galaxies.
The cosmic web is still in the process of evolving as the gravity of the dark matter pulls normal matter into large clus-ters and groups of galaxies. At the same time, the mysterious force called dark energy is causing the expansion of our universe to accelerate. Its effect is opposite the gravitational pull of the dark matter. Dark matter influences structures to collapse and form, pulling galaxies into large cluster groups; but dark energy causes accelerating expansion, pulling structures apart. (Figure credit: Visualization by F. Summers, STScI. Simulation by L. Hernquist, Harvard University and M. White, University of California at Berkeley)
Dark Matter...from page 53
Dr. Meghan Gray was born in Halifax, Nova Scotia. While studying for a B.S. at Mount Allison University in New Brunswick, Canada, her interest in an astronomical career was inspired by summer research experiences at the Dominion Astrophysical Observatory and the Canada-France-Hawaii Telescope. In 1997, she traded in the beaches of Hawaii for the cobblestones of Cambridge to pursue a Ph.D. at the University of Cambridge. She has remained in the U.K., holding postdoctoral fellowships first at the University of Edinburgh and then at the Uni-versity of Nottingham, where she is now a Science and Technology Facilities Council Advanced Research Fellow and lecturer in the School of Physics and Astronomy. Dr. Gray enjoys explaining her research on galaxy evolution to the public. She recently organized the conference “Malaysia09: Galaxy Evolution and Environment” at the University of Nottingham campus in Kuala Lumpur, Malaysia.
Dr. Catherine Heymans was born in Hertfordshire in the United Kingdom. She received a Masters in physics from the University of Edinburgh in 2000, and her Ph.D. from the University of Oxford in 2003. She has worked at the Max-Planck Institute in Heidelberg, Germany, and the University of British Columbia, Canada, and is now a senior research fellow at the University of Edinburgh. Her current work focuses on using weak gravitational lensing to understand dark matter and dark energy in the universe.
UPDATESince the original publication of this article, the STAGES team has examined in detail the galaxy residents of the Abell 901/902 cluster to observe how they are influenced by the environment in which they live. They’ve found many intriguing results, including a new population of dusty red spiral galaxies located in the outskirts of the cluster. Analysis shows the ongoing growth of clusters as field galaxies are pulled in by the strong gravitational pull of the dark matter. The team found new evidence that supports the theory that red dwarf elliptical galaxies are the remnants of those disk galaxies that have fallen in. They have also made their full multi-wavelength data set public for other researchers to investigate.
Further ReadingBarazza, F.D., et al., “Relating Basic Properties of Bright Early-type Dwarf Galaxies to Their Location in Abell
901/902,” Astronomy and Astrophysics, 508, 665–675, 2009.Gray, M.E., et al., “STAGES: the Space Telescope A901/2 Galaxy Evolution Survey,” Monthly Notices of the
Royal Astronomical Society, 393, 1275–1301, 2009.Heidermann, A., et al., “Interacting Galaxies in the A901/902 Supercluster with STAGES,” The Astrophysical
Journal, 705, 1433–1455, 2009.Wolf, C., et al., “The STAGES View of Red Spirals and Dusty Red Galaxies: Mass-dependent Quenching of
Star Formation in Cluster Infall,” Monthly Notices of the Royal Astronomical Society, 393, 1302–1323, 2009.
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Contact STScI:
Contents:Hubble Cycle 18 Proposal Selection. . . . . . . . . . . . . . . . . . . 1
The Hubble Multi-Cycle Treasury Science Program . . . . . . . 18
Optimizing Science with the Hubble Space Telescope . . . . . 22
Cosmic Origins Spectrograph News . . . . . . . . . . . . . . . . . . 25
Enabling New Science with WFC3 . . . . . . . . . . . . . . . . . . . 29
ACS Status . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
STIS Update . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Webb Update . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Wavefront Sensing and James Webb Space Telescope . . . . 35
MIRI Status . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Community Missions Office . . . . . . . . . . . . . . . . . . . . . . . . 39
MAST, Multi-mission Archive at Space Telescope . . . . . 40
Hubble Fellowship News . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Hubble Fellows, the Future is in Your Hands . . . . . . . . . . . . 44
May Symposium 2010 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Hubble Science Year in Review. . . . . . . . . . . . . . . . . . . . . . . 48
Magnetic Filaments in an Active Galaxy. . . . . . . . . . . . . . . . 49
Dark Matter and Galaxy Life in a Supercluster . . . . . . . . . . 51
Contact STScI. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Calendar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
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Cycle 18 STUC (STScI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–13 November 2009Multi-cycle Treasury deadline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 November 2009Release of Cycle 18 Call for Proposals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 December 2009Multi-cycle TAC (STScI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7–8 January 2010AURA Board (La Serena, Chile) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1–4 February 2010STIC (STScI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9–10 February 2010JWST SWG (Washington) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17–18 February 2010Cycle 18 Proposal deadline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 February 2010Young Women Science Forum for Middle and High School Girls (STScI) . . . . . . . . March 6, 2010AURA Board (Annapolis) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21–22 April 2010Cycle 18 Panel and TAC Meetings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17–21 May 2010STIC (Paris, France). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21–22 June 2010JWST SWG (Edinburgh, Scotland) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14–15 July 2010Science with Hubble III (Venice, Italy) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11–14 October 2010
Calendar
