Direct Detection of Planets Mark Clampin GSFC

Mark Clampin/GSFC Introduction Definition –Direct detection of extrasolar planets (ESPs) by imaging –Nobody has yet imaged an extrasolar planet! –Goals of talk constrained by recent HST devlopments –Discuss what might be done with existing instruments ACS, NICMOS, STIS Planet detection is a key theme of Origins Roadmap –HST has a role to play

Mark Clampin/GSFC History Detection of extra-solar planets was always a science goal for HST –However, requirement were not well understood –Brown and Burrows (1990) defined problem of detecting ESP in reflected light for HST Their conclusion was that it was unlikely –Faint Object Camera incorporated an instrument designed for the direct detection of planets Major Project Scientist GTO Program: –A nearby star survey for ESPs-  Faint Companions Bill fastie (JHU) & Dan Schroeder (Beloit) Key HST contributions have so far come from indirect observations: transit spectroscopy and astrometry

Mark Clampin/GSFC Example Programs – Cycles TMR-1C –Tereby et al. (2000) –Initially believed to be 2-3 M J planet ejected by binary system –Now believed to be a background star Schroeder et al. (2000) –Search for faint companions with WFPC2 –Adjusted to focus on Brown Dwarf survey –Surveyed 23 stars within 13 pc using 1042M filter TMR-1C, Tereby et al 2000 ) Proxima Cen (Schroeder et al. 2000)

Mark Clampin/GSFC Requirements: Summary Detection of planets in reflected light –Brown & Burrows (1990) –Jupiter analogs require contrast ratios ~10 9 –Terrestrial planet analogs require contrast ratios ~10 10 Jupiter 10 pc –10 -8 contrast 0.16” 1.6 Au star-ESP separation,  m = 20 mag –10 -9 contrast 0.5” 5 Au star-ESP separation,  m = 22.5 mag – contrast 1.6” 16 Au star-ESP separation,  m = 25 mag

Mark Clampin/GSFC Requirements From Burrows, Sudarsky, and Hubeny 2004, Astroph

Mark Clampin/GSFC What is a Coronagraph ? Lyot stop Field stop Entrance pupil Final image Incident Starlight Broadband speckle patternSpeckle pattern Courtesy

Mark Clampin/GSFC Past/Current HST Capabilities Faint Object Camera –f/288 channel with coronagraph – best design –Never used in as-designed configuration –Photon counting precluded bright target observations STIS –Partial coronagraph in direct imaging mode –Two intersection occulting bars –Bandpass defined by CCD detector (no filters) NICMOS –Camera 2 implementation –Occulter is a hole in mirror Advanced Camera for Surveys –High resolution camera: fully sampled PSF –Aberrated beam design

Mark Clampin/GSFC HST Optics Wavefront control is the primary issue in determining coronagraph performance Light is coherently diffracted by the residual polishing errors in the optics –Structure at n cycles/aperture diffracts light to n Airy radii –Mid-frequency errors 5-50 cpa are key issues for planet detection –HST WFE~18 nm mid-freq. –Apodizing masks to control diffraction have not always been sized for optimum coronagraphic performance on HST instruments HST telescope is subject to thermal variation (breathing)

Mark Clampin/GSFC Prospects with ACS The high resolution camera in the Advanced Camera for Surveys is the most recent addition to HST’s instrument complement ACS employs an “aberrated beam” coronagraph –Occulting mask is in uncorrected focal plane –Fully-sampled PSF in visible –Best performance of any operational HST coronagraph –Trade we make for performance is limited inner working angle –Two occulting masks 1.8”, and 3.0” diameter masks

Mark Clampin/GSFC ACS Coronagraph

Mark Clampin/GSFC HRC-Coronagraph Performance

Mark Clampin/GSFC HD141569A – Circumstellar Disk ACS – Clampin et al NICMOS – Weinberger et al. 1999

Mark Clampin/GSFC The challenge!

Mark Clampin/GSFC Spectral Deconvolution GTO team have a program in progress to search for planets around  Cen –Initially planned straightforward imaging program ACS Coronagraph does not achieve requirements for planet detection even with PSF subtraction Employ technique developed by Sparks & Ford (2003) –Spectral deconvolution –ACS lends itself to this technique since it has a complement of ramp filters offering narrow and medium band imaging.

Mark Clampin/GSFC Spectral deconvolution Wavelength Sparks & Ford 2002 ApJ 578, 543

Mark Clampin/GSFC Narrow band coronagraphic observations HD130948: FR656N 634 nm 648 nm 663 nm 678 nm R=60

Mark Clampin/GSFC Narrow band coronagraphic observations rescaled

Mark Clampin/GSFC Processed FR656N observation

Mark Clampin/GSFC Medium band coronagraphic observations HD130948: FR914M 791 nm 863 nm 940 nm 1025 nm R  16

Mark Clampin/GSFC Processed FR914M observation

Mark Clampin/GSFC FR914M 8-point performance 5  detection W of HD (artificial stars at cardinal points)

Mark Clampin/GSFC Medium band coronagraphic observations HD130948: FR914M Spectral information: L-dwarf companion Count rates: 791 nm nm nm nm 42.

Mark Clampin/GSFC ACS Medium Band (FR914M) Coronagraphic Observations of HD130948: “Spectral Deconvolution” nm The primary is a G2V at a distance of 17.9 pc, V  nm nm nm

Spectral Deconvolution of the ACS Medium Band Coronagraphic Observations HD The L-dwarf binary is 2.64  from the primary. The binary separation is . The binary is ~ 13 mags fainter than the primary in these filters. Sparks, W. & Ford, H., “Imaging Spectroscopy for Extrasolar Planet Detection” 2002 ApJ, 578, 543 We get within square root two of the shot noise in the speckles! This should allow detection of a Jupiter around  Cen A or  Cen B.

Mark Clampin/GSFC Spectral deconvolution implementation parameters Spectral Resolution Maps onto “outer working distance” . Speckles smear if they move by /D, dark space fills in. Can still use. If     is bandpass (one spectral resolution element) and          1 +(  /D) then it follows that spectral resolution R   /  =   /(  /D) = number of Airy rings Wavelength Range Maps onto “inner working distance”. A speckle has to move by ~ ( /D) so for an inner working distance of N  Airy rings at wavelength , I.e. N  =  /(  /D), at wavelength  there are N  =  / ( 2 /D) rings. For N 1 -N 2 =1 require 2 =  (N 1 /N  ) =  (1+N 2 )/N .

Mark Clampin/GSFC Spectral deconvolution advantages Improves detection process by eliminating speckles (in data analysis: does not eliminate their shot noise). Offers detection at small values of Q; recognition of speckles. Provides robustness against systematics. Begin characterization from the outset since obtaining spectrum is implicit part of process. Maximum observing efficiency because of spectral multiplex. Automatically observe all candidates in field; obtain detection and characterization in single observation. Requires narrow or medium band imaging Next: Take advantage of dark space between speckles to improve beyond average photon detection limit

Mark Clampin/GSFC Spectral deconvolution Subtracted PSF reveals extrasolar planet at S/N=20 with Q=0.01 (Sparks & Ford 2002)

Mark Clampin/GSFC  Cen: preliminary results W. Sparks and R. White & ACS Science Team ACS offers opportunity to apply this technique to a very small number of nearby stars where the separation and  m are favorable  Cen is the most obvious candidate

Mark Clampin/GSFC  Cen: preliminary results W. Sparks and R. White & ACS Science Team Preliminary results showing Lucy deconvolution performed on ~10% of data set Right hand image shows example with different bands & weighted sum

Mark Clampin/GSFC STIS –Definitive summary of capabilities in Grady et al. (2003) –Does not achieve contrast levels of ACS, closer inner working angle – defined by two occulting bars

Mark Clampin/GSFC Prospects with NICMOS NICMOS coronagraph has been very effective in discovering debris disks and faint companions NICMOS offers the opportunity to pursue searches for very young “self-luminous” planets which might be detectable in the near-IR –This is a key focus of ground- based AO programs –NICMOS offers a very stable platform with superior stability for such programs –NICMOS has the benefit that it can observe closer to central star than ACS TWA6 Field:  2.5” (Schneider 2002) HD (Weinberger et al. 1999)

Mark Clampin/GSFC NICMOS Capabilities

Discovery Space Log 10 Age (years) 80M jup 14M jup JUPITER SATURN STARS (Hydrogen burning) BROWN DWARFS (Deuterium burning) PLANETS 200M jup Evolution of M Dwarf Stars, Brown Dwarfs and Giant Planets (from Adam Burrows)

Mark Clampin/GSFC NICMOS Discovery Space Key resource: –Domains of observability in the near-IR with HST/NICMOS and (Adaptive Optics Augmented) Large Ground-Based telescopes – Schneider Planet Detection capability –10 Myr can detect 1 Mj at r=2” –1 Myr can detect 1 Mj at r=1” –Bias towards planets at larger distances from star Cycle 13 saw large number of coronagraph programs awarded

Mark Clampin/GSFC Cycle 13 Survey Major program in Cycle 13 by Inseok Song et al. Survey of 116 young nearby stars The selected targets are young (<~ 50 Myr) and nearby (<~55 pc) Detectable minimum mass planets

Mark Clampin/GSFC Summary Key Science still to be done –With its current complement of instruments HST offers the possibility to: Detect young-planets with NICMOS –Could apply spectral deconvolution to NICMOS too Detect planets around a few stars with ACS if spectral deconvolution can be fully exploited Issues –Both these resources require HST’s current pointing capability –Coronagraph observations with HST carry a significant overhead to perform observations effectively Require multiple rolls & comparison stars –Significant allocations of time are required to fully exploit the ACS & NICMOS capabilities for detection of extra-solar planets

Mark Clampin/GSFC New Instrumentation HST would have an instrument optimized for detection of planetary systems –Brown et al. proposed such an instrument CODEX –CODEX employs a deformable mirror to correct mid- frequency WFE Alternative approaches are also possible – Phase and amplitude correction Labeyrie (2001) Bowers and Woodgate (2003) –Visible nulling coronagraph (Shao)

Mark Clampin/GSFC Acknowledgements Thanks to Bill Sparks, Rick White, John Krist and Inseok Song.

Mark Clampin/GSFC