polarimetric detection of dust in the exoplanet candidate ... · • 20-30% solar-type stars have...
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Polarimetric detection of dust in the exoplanet
candidate KIC-1255754b
Enric Palle, P. Miles-Paez, M.R. Zapatero-Osorio, S. Berdyugina, A. Berdyugin, V. Piirola Instituto de Astrofísica de Canarias
IAU 305, Costa Rica, 2014
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Exoplanets: What have we learned so far?
• 20-30% solar-type stars have planets • At least 1 planet per star • Multiple (rocky) planetary systems are
common • Large diversity in density (composition) of
these planets
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Goal: Detection and characterization of Earth-like planets
• Technically extremely challenging • Polarimetry can certainly help
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Stokes q and u parameters measured for HD189733b by Berdyugina et
al (2008). Note the dependence of the polarization with the planet orbital
phase
First attempts at characterizing exoplanet atmospheres with polarization
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KIC1255754b a unique planet candidate
KIC12557548b
K dwarf
V = 16
P = 15.7 h
Variable transit depths
Discovered by
Rappaport et al, 2012
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Kepler data show no regular patterns in transit depth
Deph of the transit changes with time
Deep and shallow eclipses
Most likely scenario: a small planet with a secondary cometary tail-like component
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Transit spectroscopy in the visible with OSIRIS @GTC
No color differences down to 600pp,
Constraints on the particles sizes of the planet/comet tail
Dust silicate features 0.3-0.4 micron
Alonso et al, in prep
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DIPOL-2
- DIPOL-2 was constructed in collaboration between the
Turku University and Kiepenheuer Institute fuer Sonnenphysik
- Capable of achieving the polarimetric accuracy of 10-5 simultaneously in three bands: B, V, and R
- The instrument was successfully operated at KVA-60 telescope at ORM.
- DIPOL-2 at the KVA-60 has achieved a level of precision of 7-8 x 10-6 for bright stars (3-4 Vmag ) in integration times of 2.5 to 3.5 hours
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Instrumental polarization: Pi(B) = 59±6 x 10-6 Pi(R) = 10±5 x 10-6
Observations:
- 4 datasets, 1h duration, 3 nights -Each had 24-32 cycles of exposures of 16 angles each (0 , 22.5, 45 , ..., 337.5), combined into a single polarization measurement. -Individual exp times = 20s -Images were taken with the telescope slightly defocussed.
DIPOL-2 at WHT
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Work in progress..
Linear polarimetry data folded in orbital phase
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Confirmation Observations with ISIS at the WHT
- ISIS can do broad-band linear polarimetry observations
- We set it up to use the B filter, although it is highly inefficient
- 4 observing angles
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Photometric precision
≈10 mmag
Average Transit depth
7 mmag
Photometric data folded in orbital phase
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We are unable to obtain precise enough linear polarimetry measurements
Linear polarimetry data folded in orbital phase
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Concluding remarks
- Use the right instrument to do the right observation
- We detect with high confidence polarization at the bluest wavelengths (B band) and at the right orbital phase to be associated with the detection of dust
- We have been awarded time to repeat the original measurements and confirm the phase dependence of the polarization
- We are also working on the best physical model to explain both the photometric and polarimetric observations.
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Thanks