Polarimetric study of transiting extrasolar planets

We present the results of modelling the polarization produced during planetary transits in the systems HD 189733, TrES-3, Wasp-4 and Wasp-25, using the Monte Carlo method. Polarization maxima at the limb are calculated to be ∼0.022 per cent for HD 189733 with stellar polarization according to Chandrasekhar. The polarization for the system HD 189733 of ∼0.022 per cent is close to that previously published, although this was attributed to scattering of starlight, rather than produced in transit. Using three-dimensional modelling data for the linear polarization of the Sun's continuous spectrum, the limb polarization of the solar-type stars Wasp-25 was calculated to be ∼0.00018 per cent, ∼0.00024 per cent for TrES-3 and ∼0.00016 per cent for Wasp-4 in the B band. It is noted that observations of the Sun-like stars in the Ti I 4536 Å spectral line are particularly suitable for distinguishing between different contributions to the polarization. Also, the shape of the polarization curves, at the near limb transits, can be used for obtaining the inclination of the planet orbit, as a good alternative to standard transit methods.