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UMBRAS
Distant Screens: From Extrasolar Planets to
Eclipsing the North Star
http://umbras.org http://westminsterastro.org
Ian J. E. Jordan, December 6, 2005
Space Telescope Science Institute
UMBRAS Core Investigators
• Glenn D. Starkman, Craig G. Copi
– Case Western Reserve Univ.
• Mark Kochte, Dorothy Fraquelli, F. Hamilton, Charlie Wu. Ian Jordan–Computer Sciences Corporation @ STScI
• Helen M. Hart–Applied Physics Lab
• Paul Henze, George Sauter, Erich Bender, Brian Eney, Ron Smith –Westminster Astronomical Society, Inc.
• Alfred B. Schultz, Richard Lyon, Peter Chen, Jan M. Hollis, Ken Carpenter, Jesse Leitner, Richard Burns, Scott Starin
–NASA/Goddard
• Fred Bruhweiler–CUA/IACS
• Dennis Skelton–Orbital Sciences Coproration
• Ed Rowles–Blue Horizons
• Zolt Levay–AURA
• Bryce Roberts–U.C. Berkeley
An Outline for this Evening…
• Introduction: Extrasolar planets--to date.
• History & Workings of External Occulters
• Ground Demonstration w/ WASI participation.
Successful Planet Finding Techniques
Courtesy L. Cook, exoplanets.org
Transit
Courtesy: Penn State & Alex Wolszczan
Pulsar Timing
Candidates found: ~2-50
Candidates found: ~130
Microlensing
Direct Imaging& Coronography
Candidates found: ~3
Candidates found: ~4
Candidates found: ~2
2M1207 & GQ Lupi
Ground-based & HST surveys are starting to yield direct images of planets, but these are very far away from their parent stars, very large, and/or very young.
TPF: What is the problem?
TPF: Terrestrial Planet Finder … Detect & study earth-like planets around nearby stars.
• Earth < 0.” 1 from the sun when viewed from 33-light years away
(diameter of a quarter at 50 km).
• Sol appears 10-billion (1010) times brighter than earth.
Occulter: “covering up” the star improves star-planet contrast.
Before After
COSMOS
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Carl Sagan in COSMOS Episode 7 “The Backbone of Night.”
A Brief History of Occulters
<1962 Robert Danielson, Princeton Infinite Half-plane analysis1962 Lyman Spitzer, Princeton American Scientist “Beginnings &
Future…”
1972 Su-Shu Huang, Northwestern Resurrected Spitzer’s analysis1974 Gordon Woodcock, Boeing Occulter Vehicle Design1978 Hugh S. Hudson, UCSD, et.al. Shuttle-borne Pinhole Occulter Facility1978 James Elliot, Cornell Lunar occultation for LST, Hill Orbits
1980 Carl Sagan COSMOS "Backbone of Night" episode1985 Christian Marchal, ONERA Spergel-Kasdin-like Screen Shapes
1995 Jean Schneider, Obs. de Paris SCODOTEP1997 G. Starkman, C. Copi, CWRU IRIS (opaque occulter)1998 G. Starkman, C. Copi, CWRU BOSS (apodizing occulter)1998 Schultz, Jordan, Hart, et.al. UMBRAS (feasability studies)
2001 R. Lyon, A. Schultz, et.al. Occulter + Shaped Aperture /Apodization2005 W. Cash, et.al. New Worlds Observer (Marchal occulter)
BOSS Variable Transmission Screen Occulter
What is BOSS? -- It is a different kind of occulter mission.
BOSS employs an apodizing occulter without using multiple PSF suppression stages within the telescope.
Plot & Image courtesy of BOSS team, TRW, & JPL
Telescope-Occulter Control Block Diagram
• Telescope science imager takes picture(s)
• Pictures are measured to determine occulter position
• Error signal transmitted to occulter
• Occulter adjusts position & velocity
Ambient Earth-Sun L2 Accelerations
Earth-Sun L2.20,000 km Telescope-Occulter separation, with non-sail-like telescope & occulter properties for a likely typical TPF mission.
Dif
fere
ntia
l Acc
eler
atio
n M
agni
tude
(m
/s2)
Sun-Telescope-Occulter Angle (degrees)
•Brown solid = -gravitational (earth)•Black dotted = -gravitational (sun)•Green solid = ~ solar radiation pressure•Yellow solid = -gravitational (moon)•Blue dashed = max allowed gas leakage (10%)•Orange dotted = ~ nominal solar wind
NSTAR acceleration level
Science Ceiling
Why an Occulter?
Better suppression of the stellar PSF wings even with lower wavefront quality.
ASA: WFQ = /1000
ASA + O: WFQ = /100
ASA = Apodized Square ApertureWFQ = Wave Front Quality
Point Spread Function Slices using a 4-metre Telescope
Dawes’ Limit2.4-m V-band
Dawes’ Limit8-m V-band
Discovery Space Diagram
Exoearths fainter than mV=32 not plotted.
TPF-C goal.TPF-C goal + minimal Occulter.
Exoearth mV=29.5
M1V
K3V
G0V
A5V
M3V
M4V
M7V
B6V
Alpha Cen B
Alpha Cen A
Tau Ceti
Epsilon Eridani
Epsilon Indi
Pi3 Orion
Occulter vs Alternate Method Cost
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FL = Fresnel LensFFO = Free-Flying OcculterNIFF = Free-Flying Nulling InterferometerNIM = Monolithic Nulling InterferometerLAC = Large Aperture CoronagraphULSA = Ultra-Large Sparse ApertureSIM = Space Interferometry Mission
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The New Worlds Observer/Imager Concept
Ground ‘Tests’ of Occulters
FN =W2
z⋅λW = FN ⋅z⋅λ
D∝ z
W=occulter width; z=separation; =wavelength; D=aperture.
D=4m; z=20,000 km
W=D⋅constant
D=9mm;z=100m
Ground Test Equipment
• F/5 Televue 101-mm refractor.• Masked down to 11 & 24 mm.• Optional Barlow: system f/# from 50 - 100.• Mounted atop 8” + alt/az for stability.• ST-7X, TEC-cooled, 768x512 CCD camera.• M675X laptop data acquisition/storage.• Green laser for optical alignment.
• Hand-crafted (P. Henze) occulter-rig.• 12-inch diameter light shroud tube.• Square-rail optical bench.• Mid-tube occulter placement slot.• 1- and 2-inch square occulters.• 9” 1/10th-wave flat & mirror cell (GSFC).• Alt-az mirror mount.• Red laser for optical alignment.
9” mirror
765 x 510 9- pixels, 540-mm focal length, distance ~ 95 metres
Experiment Field of View.
25-mm (~ 15 pixels) edge occulter
626-second drift.
August 7/8, 2004
Occultation Movie
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Watch for
real
diffraction
lobes!
Movie C
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19:45 November 5, 2004, Drift 6, 24-mm aperture.
Theory & Experiment: ComparisonAdmittedly, this is red and green apples, but . . . .
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• Monochromatic, • Square aperture, • No wavefront error
• Polychromatic ~ 0.5, • Circular aperture, • Atmospheric induced wavefront error, • Atmospheric smearing
Sonine 4 Apodization
Unapodization
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