Hubble Science Briefing: 25 Years of Seeing Stars …hubblesource.stsci.edu/services/events/telecons/...Hubble Science Briefing: 25 Years of Seeing Stars with the Hubble Space Telescope

Hubble Science Briefing: 25 Years of Seeing Stars with the Hubble Space Telescope

March 5, 2015

Dr. Rachel Osten

Dr. Alex Fullerton

Dr. Jay Anderson

Hubble’s Insight into the Lives of Stars Comes From:

Better image clarity: no atmosphere, no blurring means higher spatial resolution

Access to ultraviolet wavelengths: not possible from the ground

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Outline

• Rachel Osten - cool stars • Alex Fullerton - massive stars • Jay Anderson – globular clusters

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The UV spectrum of a Sun-like star

Hot gas (>10,000 K) means that many elements are ionized Hotter than the visible surface of the star (Sun=5800 K)

Linsky & Wood 1994 5


Pagano et al. 2004

Brightness

Alpha Cen A at higher spectral resolution than UV spectra from the Sun!

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Linsky & Wood 1994

Brightness

Dynamics of the atmosphere

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Brightness Time (seconds)

The changing of a star’s intensity with time on these short timescales is due to heating from flares occurring in the atmosphere of the star

Hawley et al. (2003)

0 200 400 600 800 0 200 400 600 800

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Stars Blow Bubbles in Space

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Wood et al. 1995 10


Wood et al. 2002

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Linsky et al. 2010

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Outline


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Massive Stars

Image Source: kids.britannica.com

1 Solar Mass 1 Solar Radius 1 Solar Luminosity T = 5,800 Kelvin

4 - 300 (?) Solar Masses 3,000,000 Solar Luminosities Temperature: 10,000 – 50,000 Kelvin Radius: 2 – 15 Solar Radii 30 Solar Radii T = 7,500 – 3, 600 Kelvin R = 80 – 8, 000 Solar Radii

Massive stars can be luminous because they are • hot and compact • hot and large • cool and very large

Massive stars are also luminous stars.

“Red” supergiants

The Kelvin Temperature Scale: K =5

9F -32( ) + 273.15

“Blue” supergiants

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R136

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Space Telescope Imaging Spectrograph (STIS) From a poster paper by A. Bostroem, N. Walborn, et al.

“P Cygni Profiles” tell us about mass loss via a “stellar wind”

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The Carinae Region: A Cauldron of Hot, Massive Stars

This spectacular montage was created to celebrate the 17th anniversary of Hubble’s deployment. It is composed of many separate exposures with Hubble’s Advanced Camera for Surveys (ACS) and ground-based images from the Cerro Tololo Inter-American Observatory (CTIO). For a fuller appreciation of its information content, explore the “zoomable” version: http://hubblesite.org/newscenter/archive/releases/2007/16/image/a/format/zoom/

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http://hubblesite.org/newscenter/archive/releases/2007/16/image/a/format/zoom/






η Carinae


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η Carinae

Trumpler 14


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“S-Curve” from an FGS scan of a point source.

FGS1R: HST’s Interferometer That Can!E. Nelan, R.B. Makidon and L. Nagel (STScI)

HS

T F

ine

Guid

ance

Sen

sors Introduction

The unprecedented pointing precision required by the Hubble Space Telescope (HST) motivated the design of

the Fine Guidance Sensors (FGS). These are large field of view (FOV) interferometers that are able to track the

positions of luminous objects in HST’s focal plane with ~1 millisecond of arc (mas) precision. The FGS can

also scan an object’s interferogram with sub-mas resolution. These capabilities enable the FGS to perform as a

high-precision astrometric science instrument and high resolution interferometer which can be applied to a vari-

ety of topics and objectives, including:

• Visual orbits for binary systems with separations as small as 10 mas. Detection of duplicity down to 7 mas.

• Measuring the angular size of extended objects.

• Relative astrometry at the 0.2 mas level (mV < 14.5).

• 40 Hz relative photometry (e.g., flares, occultations) with milli-mag accuracy

ReferencesBenedict, G.F. et al. 1998, AJ, 116, 429.

Elliot, J.L., Strobel, D. F., Zhu, X., Wasserman, L. H., and Franz, O. G. 1998, DPS, 30.4901.

Harrison, T.E. et al. ApJ, 515, L93.

Lattanzi, M.G., Munari, U., Whitelock, P.A., and Feast, M.W. 1997, ApJ, 485, 328.

Niemela, V.S., Shara, M.S., Wallace, D.J., Zurek, D.R. and Moffat, A.F.J. 1998, AJ, 115, 2047.

Abramowicz-Reed, L. 1997, private communication.

Transfer Mode Observing

In Transfer Mode the FGS scans an object to obtain its interferometric fringes with sub-mas resolution. This is

conceptually equivalent to imaging an object with sub-mas pixels. This makes the FGS ideal for studying binary

systems and extended objects over a large magnitude range (3.0 < mV < 16.0).

Binary Systems

Angular Diameters

Actual WFPC2 and simulated FGS Observations of a 168 mas binary system.

Simulated WFPC2 and FGS Observations of a 70 mas binary system.

Although the binary in this exam-

ple is clearly resolved by the

WFPC2 Planetary Camera (PC)

(Niemela et al. 1999), the FGS

could measure the component sep-

aration and relative brightness with

greater accuracy (± 1 mas v.

± 30 mas).

Although a PC detection would be

questionable at 70 mas, the FGS

clearly isn’t challenged in detect-

ing duplicity and measuring sepa-

rations. Detections of duplicity

down to 7 mas are possible with

the FGS.

The FGS has been used successfully to determine the

angular diameters of non-point sources. the example given

in the figure at left shows the Transfer Function of a Mira-

type variable (Lattanzi et al. 1997) superposed on the S-

Curve of a point source. The extended source - a disk of

78 ± 2 mas - is clearly distinguishable from a point source.

In addition to stellar disks, the FGS has also been used to

determine the angular sizes of Active Galactic Nuclei

(AGNs), asteroids, and extragalactic star formation

regions.

Position Mode Observing

As an astrometer, the FGS can measure the relative positions of stars in its Field of View (FOV) with a per-

observation precision of ~ 1 mas. Key characteristics of observing in Position Mode include:

• A large (69 arcmin2) Field of View (FOV).

• A large dynamic range (3.0 < mV < 16.0).

• Binary and variable star astrometry.

• Down to 0.2 mas relative astrometry for multi-epoch observing programs (achievable in ~ 12 HST orbits)

In Position Mode, the FGS has been successfully used to measure astrometric parallaxes to a number of targets,

including the nearby dwarfs Proxima Centauri and Barnards Star (Benedict et al. 1998), and the dwarf novae

SS Aurigae, SS Cygni and U Geminorum (Harrison et al. 1998).

6.6

10.6

13.1

7.2

15.2

15.4

14.3

13.6

16.1

14.9

12.1

9.2

10.8

15.3

11.9

11.8

11.6

15.9

15.113.7

14.1

13.6

The FGS FOV and a “Typical” Astrometric Star Field.

In the above example, the science target is denoted by the central triangle, while astrometric reference stars are

denoted by circles. Magnitudes of individual objects are given beside each target. Note the magnitude range, from

mV = 6.6 to mV = 16.1.

Relative Photometry

While conducting Position Mode observations, FGS3 successfully captured a flare event on Proxima Centauri

(Benedict et al. 1998). In another series of observations, the FGS observed the occultation of a 10.6 magnitude

star by the Neptunian moon Triton (Elliot et al. 1998).

The absolute FGS photometric response has been stable to 2% over the past seven years (Abramowicz-Reed

1997). For relative photometry, on time scales of orbits, the FGS is stable to about 1 milli-magnitude at a rate of

40 Hz. This affords an opportunity for 0.1 to 0.2% time-series photometry for most tar gets.

Flare Outburst on Proxima Centauri Stellar Occultation by the Moon Triton

STScI is Operated by the Association of Universities for Research in Astronomy, Inc., for the National Aeronautics and Space Ad ministration.

Cycle 9 Call for Proposals

The HST Cycle 9 Call for Proposals will be released in June 1999, with a GO proposal deadline of Friday ,

10 Sep 1999 at 8:00PM EST. Propose early. Propose often. Propose wisely!

From the FGS Instrument Handbook 24

HD 93129A Trumpler 14

Palomar Digital Sky Survey

Component A is also a binary!

HD 93129A

HD 93129B

European Southern Observatory Science Release 0947 Very Large Telescope + Multi-Conjugate Adaptive Optics Demonstrator

ESO VLT: Aperture Mask with Adaptive Optics Sana et al. 2014 Astrophysical Journal Supplement

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NGC 3603 HST/ACS

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Outline


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Plan

(1) Globular Clusters before HST

(2) Globular Clusters with HST

(3) Globular Clusters with 25 years of HST

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Globular Clusters • “Textbook” simple stellar populations

– Formed stars early

– Single cloud, single metallicity, single age

– Not large enough to self-enrich

– Continue orbiting in spheroid of Galaxy

• Perfect fossil

laboratories

to evaluate

stellar evolution

GC

GC

GC

GC GC

NGC4013(NOAO) 29

ω Centauri

project-nightflight.net

Central Field

Early Release Field 30

http://hubblesite.org/newscenter/archive/releases/2010/28/ 31


What Astronomers see…

























1) Main

Sequence 2) SubGiant

Branch

3) Red Giant

Branch

4) Horizontal

Branch

5) White

Dwarf

Sequence



Easy to identify stars… RGB

WDs

SGB

HB

MSTO

Red Dwarfs

BSs

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More metals

More Helium

Age

Red Giant Branch

A

B

C One line means: same age same metallicity same distance same small cloud

Stellar

Populations

“Isochrone”

“test of good photometry”

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Omega N6397 47T

Omega Cen NGC6397 47 Tuc

Extra sequences

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Plan




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Globular Cluster or Dwarf Spheroidal?

Cambridge, UK 2001

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Stellar

Populations

More metals

More Helium

Age

Inversion!

More metals

metal poor

intermediate

metal rich

Red Giant Branch

Similar to galaxies…

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Is Omega Cen a GC? Could the textbook globular cluster not be one?

47Tuc

N2808

N6656 N6388

OmCen

®

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Is Omega Cen a globular?

Are there any globular clusters? Questions to answer: 1) How does the enrichment happen? 2) Why are they all so different? 3) What connection is there between clusters and galaxies? 4) Any relevance for star formation going on today?

NGC2808

NGC6652

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Plan




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GCs with Hubble Over Time

• Set up new experiments

– Probe deeper

– Probe more broadly

• Use new detectors

– Better sensitivity, resolution

– Better filter sets

• Things move!

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Anderson et al 2002

Initial 2-seq Discovery on

Main Sequence (WF/PC2)

Bellini 2014 (WFC3/UVIS)

Latest results all over the

diagram! 10 Seqs!

ω Centauri

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D’Antona 2005 (ACS)

Initial Discovery

Bellini et al in prep

(WFC3/UVIS)

NGC2808

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2002 ACS H-alpha

Motions in ω Centauri

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2015 WFC3/UVIS F606W

Motions in ω Centauri

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2015 WFC3/UVIS F606W

MOTIONS OVER 13 YEARS Motions in ω Centauri

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Proper

Motions

Important Qs • Formation hints

• Are GCs just little galaxies?

• Do they have medium-sized BHs?

• How did the big BHs form in big galaxies?

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Plan




(4) Globular Clusters in the next 25 years…

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View to the Future: the James Webb Space Telescope

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View to the Future: the James Webb Space Telescope

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Documents

Hubble Science Briefing: 25 Years of Seeing Stars …hubblesource.stsci.edu/services/events/telecons/...Hubble Science Briefing: 25 Years of Seeing Stars with the Hubble Space Telescope