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