The SPHERE/ZIMPOL polarimeter for extra-solar planetary systems Hans Martin SCHMID, ETH Zurich

1. The SPHERE/ZIMPOL polarimeter for extra-solar planetary systems Hans Martin SCHMID, ETH Zurich and many collaborators in the SPHERE consortium IPAGGrenoble, 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

2. 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

3. Why polarimetry? Reflected light from disks is polarized

4. If not, simulate! simulated PSF 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 12 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”

5. 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, Hα, 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 < 5pc • characterize scattered light from circumstellar disks your high resolution and high contrast polarimetric imager at the VLT What about your science?

6. SPHERE-Design

7. Jan 2012  Dec 2012

8. synchronization (kHz) polarizer modulator 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)

9. 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 Nasmyth focus pol.-switch derotator AO adaptive optics compensator plate near-IR instruments λ>0.95μλ<0.9μ imaging polarimeter coronagraph BS BS WFS wave front sensor

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

11. 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

12. 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

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

14. 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

15. 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 5% sol. system 7% SOFI 3% 7% NACO stellar magn. fields 38% 5% CS scatt. 9% EFOSC 14% AGN scatt. 17% FORS1 72% GRB / SN 22% Message: Only well designed polarimetric systems produce a lot of science

16. Thank you