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

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

Goal: Detection and characterization of Earth-like planets

• Technically extremely challenging • Polarimetry can certainly help

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

KIC1255754b a unique planet candidate

KIC12557548b

K dwarf

V = 16

P = 15.7 h

Variable transit depths

Discovered by

Rappaport et al, 2012

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

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

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

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

Work in progress..

Linear polarimetry data folded in orbital phase

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

Photometric precision

≈10 mmag

Average Transit depth

7 mmag

Photometric data folded in orbital phase

We are unable to obtain precise enough linear polarimetry measurements

Linear polarimetry data folded in orbital phase

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.

Thanks