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

Why polarimetry? Reflected light from disks is polarized

If not, simulate! simulated PSF log(counts) photon noise level planet signal PSF 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 Why polarimetry? Differential technique for detecting planets

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 nm filters: broad-band R,I, …; narrow band CH 4, KI…; line filters, Hα, OI…. Polarimetric sensitivity SPHERE Extreme AO system (9 mag star), Strehl up to 50% for nm coronagraphy (Lyot coronagraphs, 4QPM) IRDIS: polarimetry in the 1 – 2.2 µm range Goals: polarization contrast limit for bright stars detect planets around nearby stars d < 5pc 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

synchronization (kHz) modulator polarizer demodulating CCD detector S(t)I(t) S polarization signal modulated polarization signal modulated intensity signal 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)

Polarimeter implementation SPHERE mutual constraints: polarimeter should not affect the AO AO should not destroy polarization 1. telescope polarization compensated with rotating λ/2-plate and M4 mirror 2. instrument polarization calibrated with pol. switch 3. Instrument polarization compensated by inclined plate telescope AO adaptive optics near-IR instruments WFS wave front sensor coronagraph BS pol.-switch λ>0.95μ λ<0.9μ imaging polarimeter Nasmyth focus derotator compensator plate

HWP1 Pol.Cal. HWP2 M4 derotator BS pol.comp. Pol.Cal filters FLC Mod. HWPZ Polarimetric Details

SPHERE/ZIMPOL concept Telescope polarization corrected with HWP1 and mirror M4 HWP2 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

Lets 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 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

stellar magn. fields 38% GRB / SN 22% AGN scatt. 17% CS scatt. 9% sol. system other 7% FORS1 72% EFOSC 14% NACO SOFI other 5% 3% 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 Message: Only well designed polarimetric systems produce a lot of science

Thank you