Temperature stratification of the atmosphere of Arcturus

TL;DR

This study models the atmosphere of Arcturus using spectral line synthesis, revealing continuum underestimations and providing a detailed temperature stratification, aligning with previous fundamental parameters.

Contribution

It introduces a one-dimensional LTE model of Arcturus's atmosphere based on Ca II line wings, offering a detailed temperature stratification and continuum correction factors.

Findings

Continuum in Arcturus underestimated by 12% in atlases.

UV absorption deficit in Arcturus is 43%.

Model parameters match previous fundamental estimates.

Abstract

A brief overview of the results of the investigations of the red giant star Arcturus is given. One-dimensional LTE modeling of the atmospheres of Arcturus and the Sun as a star is carried out on the basis of synthesis of the extended wings of the H and K Ca II lines. It is found that the local continuum in this spectral region is underestimated by an average of 12% in the atlases of Arcturus. The average deficit in UV absorption amounts to 43% for Arcturus whereas it is 9% for the Sun. For Arcturus the correction factor to the continuum opacity at the wavelengths of 390.0, 392.5, 395.0, 398.0, and 400.0 nm equals 2.20, 1.90, 1.70, 1.55, and 1.45. The model atmosphere of Arcturus obtained from the best-fit of the wings of the H and K Ca II lines corresponds to the model atmosphere with the fundamental parameters T_eff = 4286 K, log g = 1.66, and [Fe/H]=-0.52 derived by Ramirez and Allende Prieto (2011). The temperature stratification of Arcturus' atmosphere is presented in tabular form. To obtain more accurate temperature stratification in the future, we need a high spectral resolution spectrum calibrated to absolute fluxes with high accuracy.