Center-to-limb polarization in continuum spectra of F, G, K stars^⋆

¹ Kiepenheuer-Institut für Sonnenphysik (KIS), Schöneckstrasse 6, 79104 Freiburg, Germany
e-mail: kostogryz@kis.uni-freiburg.de; sveta@kis.uni-freiburg.de
² Main Astronomical Observatory of NAS of Ukraine, Zabolotnoho str. 27, 03680 Kyiv, Ukraine
³ NASA Astrobiology Institute, Institute for Astronomy, University of Hawaii, Honolulu, HI 96822, USA

Received: 21 August 2014
Accepted: 23 December 2014

Abstract

Context. Scattering and absorption processes in stellar atmosphere affect the center-to-limb variations of the intensity (CLVI) and the linear polarization (CLVP) of stellar radiation.

Aims. There are several theoretical and observational studies of CLVI using different stellar models, however, most studies of CLVP have concentrated on the solar atmosphere and have not considered the CLVP in cooler non-gray stellar atmospheres at all. In this paper, we present a theoretical study of the CLV of the intensity and the linear polarization in continuum spectra of different spectral type stars.

Methods. We solve the radiative transfer equations for polarized light iteratively assuming no magnetic field and considering a plane-parallel model atmospheres and various opacities.

Results. We calculate the CLVI and the CLVP for Phoenix stellar model atmospheres for the range of effective temperatures (4500 K–6900 K), gravities (log g = 3.0−5.0), and wavelengths (4000–7000 Å), which are tabulated and available at the CDS. In addition, we present several tests of our code and compare our results with measurements and calculations of CLVI and the CLVP for the Sun. The resulting CLVI are fitted with polynomials and their coefficients are presented in this paper.

Conclusions. For the stellar model atmospheres with lower gravity and effective temperature the CLVP is larger.