The SPHEREZIMPOL polarimeter for extrasolar planetary systems Hans

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

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 > 40 % at poles p ~ 5 -10 % at equator p ~ 19 % integrated Jupiter in red light p > 40% at poles p < 5% at equator p ~ 11% integrated

Why polarimetry? Reflected light from disks is polarized

Why polarimetry? Differential technique for detecting planets 12 basic problem: planet much fainter than residual PSF halo! PSF 10 If not, simulate! log(counts) 8 simulated PSF 6 photon noise level 4 planet signal 2 0. 0” 0. 1” 0. 2” 0. 3” 0. 4” 0. 5” differential technique: (speckle rejection) reflection from planets and disks produce a polarization signal on top of the unpolarized PSF from the central star

Polarimetry with VLT / SPHERE ZIMPOL (Zurich Imaging Polarimeter) • Fo. V (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 CH 4, KI…; line filters, Hα, OI…. • Polarimetric sensitivity 10 -5 SPHERE • Extreme AO system (9 mag star), Strehl up to 50% for 600 -900 nm • coronagraphy (Lyot coronagraphs, 4 QPM) • IRDIS: polarimetry in the 1 – 2. 2 µm range Goals: • polarization contrast limit 10 -8 for bright stars • detect planets around nearby stars d < 5 pc • characterize scattered light from circumstellar disks your high resolution and high contrast polarimetric imager at the VLT What about your science?

SPHERE-Design

Jan 2012 Dec 2012

ZIMPOL: basic polarimetric principle (fast modulation) synchronization (k. Hz) polarizer modulator demodulating CCD detector S polarization S(t) modulated I(t) modulated signal polarization signal intensity signal 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)

Polarimeter implementation SPHERE mutual constraints: • polarimeter should not affect the AO • AO should not destroy polarization telescope Nasmyth focus pol. -switch derotator AO 1. telescope polarization compensated with rotating λ/2 -plate and M 4 mirror 2. instrument polarization calibrated with pol. switch 3. Instrument polarization compensated by inclined plate adaptive optics compensator plate near-IR instruments λ>0. 95μ λ<0. 9μ BS BS WFS wave front sensor coronagraph imaging polarimeter

Polarimetric Details derotator HWP 1 HWP 2 M 4 Pol. Cal. pol. comp. filters HWPZ Pol. Cal FLC Mod. BS

SPHERE/ZIMPOL concept • Telescope polarization corrected with HWP 1 and mirror M 4 • HWP 2 is used – as polarization switch to separate instrument polarization and sky+telescope 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

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 – – – AO+C polarization efficiency AO+C instrument polarization AO+C polarization crosstalk ZIMPOL modulation crosstalk Telescope crosstalk

Let‘s think big: ZIMPOL-SPHERE/VLT is just a test for EPOL-EPICS/E-ELT

ZIMPOL EPOL „optimum“ concept HWP near intermediate focus - rotates polarization from sky into the direction (p or s) of M 4, M 5 - 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 M 6 - else variable cross talks are introduced - else switch calibration is compromised no M 6

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 sol. system 7% 7% CS scatt. 9% stellar magn. fields 38% AGN scatt. 17% GRB / SN 22% Message: other 5% SOFI 3% NACO 5% EFOSC 14% FORS 1 72% Only well designed polarimetric systems produce a lot of science

Thank you