Polarimetry of extrasolar planets

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• Polarimetry of extra-solar planets
• Hans Martin Schmid, Daniel Gisler, Franco Joos,
  Christian Thalmann,
• Institute of Astronomy, ETH Zurich
• ESO PF consortium, ESO EPICS working group
• Goal Direct detection of photons from
  extra-solar planets
• (from the ground)
• Requirements for ground-based instrument
• Large telescope diffraction limit (2-30 mas),
  faint exo-planets
• Extreme adaptive optics to correct well for
  the smearing due to the atmospheric
  turbulence
• Stellar coronagraph to block the light from
  the central star, and
• to avoid detector saturation
• Differential technique to find planet in
  residual light of the very
• bright star
• ? differential spectroscopy (CH4-bands)

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Example Sun Jupiter system at 5 pc
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X-AO
tiny planetary signal in bumpy and variable PSF
halo
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Solar system planets surface properties
p(90) f(90) rocky Mercury 5-10
low Mars 5-10 low cloudy (little
Rayleigh scatt.) Venus lt5 () high
Saturn lt5 high cloudy and Rayleigh
scatt. Jupiter 5-20 high Earth
5-20 high strong Rayleigh scattering Uranus
gt15 med. Neptune gt15 med. Titan
50 med.
polarization p(90) vs. reflectivity f(90)
R-band
from Schmid et al. 2005
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Polarimeter implementation in a planet finder
instrument

• mutual constraints
• Polarimeter should not affect AO
• system and other instrument parts
• AO design, telescope, etc. should
• not destroy polarization signal
• VLT planet finder (design study)
• OWL EPICS (concept study)

telescope
pol.-switch
AO adaptive optics
near-IR instruments
?gt0.95µ ?lt0.9µ
imaging polarimeter
coronagraph
BS
BS
WFS wave front sensor
to be build by ETH
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Status of the PF-project PF VLT 2nd generation
instrument 2001 call for proposals 2003/2004
two competing phase A studies 2005 merging of
the two concepts and consortia early 2006 start
design phase 2010 first light
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• OWL ESOs 100m ELT project
• (highest priority for ESO)
• 2005
• telescope feasibility studies
• instrument concept studies
• EPICS planetary camera with
• polarimetric mode

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Expected performance for VLT and
OWL Polarization contrast Cpol p
fplanet/fstar p(a) f(a) Rp2/dp2
VLT
OWL

• Assumptions
• solar system analog at 5pc
• integration 4h
• perfect Lyot coronagraph
• R-band observation
• photon noise limit reached
• ? residual speckle noise negligible
• ? 10-5 polarimetric precision reached