Atmospheric dynamics in carbon-rich Miras. I. Model atmospheres and synthetic line profiles

TL;DR

This paper develops dynamic model atmospheres for carbon-rich Mira variables, generating synthetic spectra that replicate observed molecular line profile variations caused by pulsation-driven atmospheric dynamics.

Contribution

It introduces a new approach to modeling Mira atmospheres with velocity effects, producing synthetic spectra that match observed line profile behaviors.

Findings

Synthetic line profiles qualitatively match observed variations.

Models reproduce the influence of gas velocities on spectral lines.

Line profiles from different depths show expected pulsation effects.

Abstract

Atmospheres of evolved AGB stars are heavily affected by pulsation, dust formation and mass loss, and they can become very extended. Time series of observed high-resolution spectra proved to be a useful tool to study atmospheric dynamics throughout the outer layers of these pulsating red giants. Originating at various depths, different molecular spectral lines observed in the near-infrared can be used to probe gas velocities there for different phases during the lightcycle. Dynamic model atmospheres are needed to represent the complicated structures of Mira variables properly. An important aspect which should be reproduced by the models is the variation of line profiles due to the influence of gas velocities. Based on a dynamic model, synthetic spectra (containing CO and CN lines) were calculated, using an LTE radiative transfer code that includes velocity effects. It is shown that profiles of lines that sample different depths qualitatively reproduce the behaviour expected from observations.