Polarimetric study of transiting extrasolar planets

Abstract

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.

Polarization in Exoplanetary Systems Caused by Transits, Grazing Transits, and Starspots

“…Obviously, the latter approximation is too rough to predict the observational values of transit polarization. Thus, Frantseva et al (2012), assuming solar limb polarization for HD 189733, obtained the polarization that is different by almost two orders of magnitude as compared to Kostogryz et al (2011), showing the importance of knowing the intrinsic stellar polarization.…”

“…They also explored the cases of K-M-T dwarfs with a simplified limb polarization approximation and suggested that in favorable situations ground-based polarimetry should be able to detect Earth-like planets orbiting these stars. Kostogryz et al (2011) using the same Monte Carlo technique, simulated the transit polarization for several objects with high planet-to-star radii ratio. For the TrES-3, WASP-4 and WASP-25 systems with G spectral type host stars the modelled solar limb polarization (Trujillo Bueno & Shchukina 2009) was chosen, while for one of the brightest transit exoplanetary system HD 189733 (K spectral type) pure scattering atmosphere approximation (Chandrasekhar 1960) was applied.…”

Polarimetry as a tool to find and characterise habitable planets orbiting white dwarfs

“…Similarly, Lucas et al (2012) failed to detect polarimetric variations in two other promising systems hosting hot-Jupiters, 55 Cnc and τ Boo, reaching accuracy limits of 5 × 10 −6 . Kostogryz et al (2011) attribute the detection of Berdyugina et al (2011) to (stellar) polarisation caused at the limb during planetary transit, but the correct interpretation remains unclear.…”

Traces of exomoons in computed flux and polarization phase curves of starlight reflected by exoplanets

“…Despite not yet having been exploited, great hope is placed in the polarimetry capabilities of current and future telescopes as powerful tools for detecting and characterizing exoplanets (see Seager et al 2000;Saar & Seager 2003;Stam 2003Stam , 2008Stam et al 2004;Snik & Keller 2013). Previous works in this field involve the modeling of stellar polarization during planetary transits (Carciofi & Magalhães 2005;Kostogryz et al 2011Kostogryz et al , 2015Wiktorowicz & Laughlin 2014;Sengupta 2016), the modeling of light curves and polarization of starlight reflected signals in the visible range of Earth-like planets (Stam 2008;Karalidi et al 2012;Rossi & Stam 2017) and giant Jupiter-like planets (Seager et al 2000; A&A 618, A162 (2018) Stam et al 2004), as well as the modeling of exoplanetary atmospheres in the infrared (De Kok et al 2011;Marley & Sengupta 2011), which demonstrated the usefulness of direct observations for exoplanet characterization. More recently, Bott et al (2016) reported linear polarization observations of the hot Jupiter system HD 189733, and Ginski et al (2018) announced the detection of planetary thermal radiation that is polarized upon reflection by circumstellar dust.…”