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

TL;DR

This study theoretically models the center-to-limb intensity and polarization variations in continuum spectra of F, G, and K stars, expanding understanding beyond solar atmospheres to cooler stars using polarized radiative transfer calculations.

Contribution

It provides the first comprehensive theoretical calculations of CLVP in non-gray stellar atmospheres across various spectral types, temperatures, and gravities, with results available in a public database.

Findings

CLVP increases with lower gravity and temperature.

Calculated CLVI and CLVP are fitted with polynomial coefficients.

Results are validated against solar measurements.

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 (4500K - 6900K), gravities (log g = 3.0 - 5.0), and wavelengths (4000 - 7000 {\AA}), which are tabulated and available at the Strasbourg astronomical Data Center (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.