Center-to-limb variation of the continuum intensity and linear polarization of stars with transiting exoplanets
| 1Shchukina, NG, 2Trujillo, B, 1Vasilieva, IE, 3Frantseva, KV 1Main Astronomical Observatory of the National Academy of Sciences of Ukraine, Kyiv, Ukraine 2Instituto de Astrofisica de Canarias, Tenerife, Spain 3Kapteyn Astronomical Institute, University of Groningen, Groningen, The Netherlands |
| Kinemat. fiz. nebesnyh tel (Online) 2017, 33(4):29-50 |
| https://doi.org/10.15407/kfnt2017.04.029 |
| Start Page: Physics of Stars and Interstellar Medium |
| Language: Russian |
Abstract: The limb darkening and the center-to-limb variation of the continuum polarization is calculated for a grid of one-dimensional stellar model atmospheres and for a wavelength range between 300 nm — 950 nm. Model parameters match those of the transiting stars taken from the NASA exoplanet archive. The limb darkening of the continuum radiation for these stars is shown to decrease with their effective temperature. For the λ 370 nm wavelength, which corresponds to the maximum of the Johnson-Cousins UX filter, the limb darkering of the transiting stars are enclosed in a range between 0.03 and 0.3. In contrast, the continuum linear polarization depends not only on the effective temperature of the star, but also on its gravity and metallicity. Its value decreases for increasing values of these parameters. At the UX band maximum the linear polarization of stars with transiting planets amounts to about 4 %, while the minimum value is about 0.3 %. The continuum limb darkening and the linear polarization decreases rapidly with wavelength. At the R band maximum (λ = 700 nm) the linear polarization close to the limb is in fact two orders of magnitude smaller than in the UX band. The center-to-limb variation of the continuum intensity and the linear polarization of the stars with transiting planets can be approximated, respectively, by polynomials of fourth and sixth degree. The coefficients of the polynomials, as well as the IDL procedures for reading them, are available in electronic form. It is shown that there are two classes of stars with high linear polarization at the limb. The first one consists of cold dwarfs. Their typical representatives are HATS-6, Kepler-45, as well as all the stars with similar parameters. The second class of stars includes hotter giants and subgiants. Among them we have CoRoT-28, Kepler-91 and the group of stars with effective temperatures and gravities around 5000 K and 3.5, respectively. |
| Keywords: limb darkening, polarization, transiting stars |
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