The SPHERE/ZIMPOL polarimeter for extra-solar planetary systems

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The SPHERE/ZIMPOL polarimeter for extra-solar
planetary systems Hans Martin SCHMID, ETH
Zurich and many collaborators in the SPHERE
consortium IPAG Grenoble, F
J.L. Beuzit, D. Mouillet, P. Puget, J.
Charton, G. Chauvin,
J.C. Augerau, F.
Menard, P. Martinez, A. Eggenberger, et al.
ETH Zurich, CH D. Gisler, A.
Bazzon, P. Steiner, F. Joos, et al., ASTRON, NL
R. Rolfsema, J. Pragt, F.
Rigal, J. Kragt, et al. Univ. of Amsterdam NL
C. Domink, Ch. Thalmann, R. Waters (SRON),
Leiden University NL C. Keller, F.
Snik MPIA Heidelberg, D M. Feldt, A.
Pavlov, Th. Henning, R. Lenzen, et al. LAM
Marseille F K. Dohlen, M. Langlois
(now Lyon), et al. ESO, Garching,
M. Kasper, M. Downing, S. Deires, N. Hubin, et
al. LESIA, Meudon, F A. Boccaletti, et
al. ONERA, F T. Fusco et
al. INAF-Padova, I A. Baruffolo,
R. Gratton, S. Desidera, et al. Obs. de Geneve,
CH F. Wildi, S. Udry, et al. 1. Why
polarimetry? 2. Polarimetric concept for
SPHERE/ZIMPOL 3. Outlook to EPOL / E-ELT
Planet Finder
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Why polarimetry? Reflected light from planets is
polarized

• at the poles
• haze scattering
• at equator
• cloud reflection
• thin layer of Rayleigh scattering

Jupiter in blue light p gt 40 at poles p 5-10
at equator p 19 integrated
Jupiter in red light p gt 40 at poles p lt 5 at
equator p 11 integrated
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Why polarimetry? Reflected light from disks is
polarized
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Why polarimetry? Differential technique for
detecting planets

• basic problem
• planet much fainter than
• residual PSF halo!
• differential technique (speckle rejection)
• reflection from planets and disks produce a
  polarization signal
• on top of the unpolarized PSF from the
  central star

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PSF
10
8
log(counts)
6
photon noise level
4
planet signal
2
0.0 0.1 0.2 0.3 0.4
0.5
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Polarimetry with VLT / SPHERE

• ZIMPOL (Zurich Imaging Polarimeter)
• FoV (detector) 3.5 x 3.5 arcsec resolution of
  15 mas at 600 nm
• wavelength range 550-890 nm
• filters broad-band R,I, narrow band CH4, KI
  line filters, Ha, OI.
• Polarimetric sensitivity 10 -5
• SPHERE
• Extreme AO system (9mag star), Strehl up to 50
  for 600-900 nm
• coronagraphy (Lyot coronagraphs, 4QPM)
• IRDIS polarimetry in the 1 2.2 µm range
• Goals
• polarization contrast limit 10-8 for bright stars
• detect planets around nearby stars d lt 5pc
• characterize scattered light from circumstellar
  disks
• your high resolution and high contrast
  polarimetric imager at the VLT
• ? What about your science?

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SPHERE-Design
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Jan 2012 ? Dec 2012
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ZIMPOL basic polarimetric principle (fast
modulation)

• Advantages
• images of two opposite polarization modes are
  created almost simultaneously
• ? modulation faster than seeing variations
• both images are recorded with same pixel
• both images are subject to almost exactly the
  same aberrations
• integration over many modulation cycles without
  readout (low RON)

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Polarimeter implementation SPHERE

• mutual constraints
• polarimeter should not affect the AO
• AO should not destroy polarization
• 1. telescope polarization compensated with
  rotating ?/2-plate and M4 mirror
• 2. instrument polarization calibrated with pol.
  switch
• 3. Instrument polarization compensated by
  inclined plate

telescope
Nasmyth focus
pol.-switch
derotator
AO adaptive optics
compensator plate
near-IR instruments
?gt0.95µ ?lt0.9µ
imaging polarimeter
coronagraph
BS
BS
WFS wave front sensor
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Polarimetric Details
derotator
HWP1
HWP2
M4
Pol.Cal.
filters
pol.comp.
HWPZ
FLC Mod.
BS
Pol.Cal
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• SPHERE/ZIMPOL concept
• Telescope polarization corrected with HWP1 and
  mirror M4
• HWP2 is used
• as polarization switch to
• separate instrument
• polarization and
• skytelescope polarization
• to orientate the selected
• polarization into the correct
• direction for the derotator
• The derotator polarization is corrected with a
  (co-rotating) polarization compensator
• HWPz rotates the polarization into the ZIMPOL
  system
• ZIMPOL performs the high precision measurement

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• ZIMPOL/SPHERE calibration plan
• for (user-friendly) data reduction pipeline
• Science Calibrations
• Astrometric calibrations
• Photometric calibrations
• Telescope polarization calibrations (unpolarized
  standard stars)
• Telescope zero point polarization angle
  (polarized standard stars)
• Technical Calibrations
• Bias
• Dark
• Intensity flat (bad pixels)
• Sky flat
• Modulation/demodulation efficiency
• Instrument monitoring
• AOC polarization efficiency
• AOC instrument polarization

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Lets think big ZIMPOL-SPHERE/VLT is just a test
for EPOL-EPICS/E-ELT
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ZIMPOL ? EPOL optimum concept

• HWP near intermediate focus
• - rotates polarization from sky into the
• direction (p or s) of M4, M5
• polarization switch (/--) and allows
• a polarimetric (self)-calibration of system
• HWP near Nasmyh focus
• - rotates sky and telescope polarization
• into direction of instrument plane
• No M6
• else variable cross talks are introduced
• else switch calibration is compromised

no M6
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Publications survey 2000 to 2006 (Schmid 2007,
ESO calibration workshop) on polarimetric
observations with ESO telescopes 58 refereed
papers Distribution of polarimetric papers with
respect to scientific topic
instrument used
other
other
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sol. system
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SOFI
3
7
NACO
stellar magn. fields 38
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CS scatt. 9
EFOSC 14
AGN scatt. 17
FORS1 72
GRB / SN 22
Message Only well designed polarimetric systems
produce a lot of science
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• Thank you