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

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. SnikMPIA 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 polesp ~ 5-10 % at equatorp ~ 19 % integrated

Jupiter in red light p > 40% at polesp < 5% at equatorp ~ 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

0.0” 0.1” 0.2” 0.3” 0.4” 0.5”

log(

coun

ts)

12

2

10

4

6

8

photon noise level

planet signal

PSF basic problem:

planet much fainter thanresidual 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 / SPHEREZIMPOL (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?

SPHERE-Design

Jan 2012 Dec 2012

synchronization (kHz)

modulator

polarizer

demodulating CCD detector

S(t) I(t)Spolarization signal

modulatedpolarization signal

modulatedintensitysignal

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 SPHEREmutual 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-IRinstruments

WFSwave front sensor

coronagraphBS BS

pol.-switch

λ>0.95μ λ<0.9μ imagingpolarimeter

Nasmyth focus

derotator

compensator plate

HWP1

Pol.Cal.

HWP2

M4

derotator

BS

pol.comp.

Pol.Cal

filters

FLCMod.

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

pQ = Q/I = (I0–I90)/(I0+I90)

Pol

ariz

atio

n pQ

[%]

time0.0

0.4

0.3

0.2

0.1

– 0.1

pQ(inst)

+pQ(tel.+sky)

–pQ(tel.+sky)

pQ = Q/I = (I0–I90)/(I0+I90)

Pol

ariz

atio

n pQ

[%]

time0.0

0.4

0.3

0.2

0.1

– 0.1

pQ(inst)

+pQ(tel.+sky)

–pQ(tel.+sky)

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“ conceptHWP 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 / SN22%

AGN scatt.17%

CS scatt. 9%

sol. system

other

7%7%

FORS172%

EFOSC14%

NACO

SOFIother

5%

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