Teff and log g dependence of velocity fields in M-stars

TL;DR

This study investigates how velocity fields in M-star atmospheres depend on temperature and gravity, providing quantitative micro- and macro-turbulent velocities for improved spectral modeling.

Contribution

It offers the first detailed characterization of velocity fields in M-star models across a range of Teff and log g, linking hydrodynamics to spectral synthesis parameters.

Findings

Velocity amplitudes increase with decreasing log g and increasing Teff.

Micro- and macro-turbulent velocities vary from ~100 m/s to ~1000 m/s depending on model parameters.

Velocity fields strongly depend on stellar parameters, affecting spectral line broadening.

Abstract

We present an investigation of velocity fields in early to late M-type hydrodynamic stellar atmosphere models. These velocities will be expressed in classical terms of micro- and macro-turbulent velocities for usage in 1D spectral synthesis. The M-star model parameters range between log g of 3.0 - 5.0 and Teff of 2500 K - 4000 K. We characterize the Teff- and log g-dependence of the hydrodynamical velocity fields in these models with a binning method, and for the determination of micro-turbulent velocities, the Curve of Growth method is used. The macro-turbulent velocities are obtained by convolutions with Gaussian profiles. Velocity fields in M-stars strongly depend on log g and Teff. Their velocity amplitudes increase with decreasing log g and increasing Teff. The 3D hydrodynamical and 1D macro-turbulent velocities range from ~100 m/s for cool high gravity models to ~ 800 m/s - 1000 m/s for hot models or models with low log g. The micro-turbulent velocities range in the order of ~100 m/s for cool models, to ~600 m/s for hot or low log g models. Our M-star structure models are calculated with the 3D radiative-hydrodynamics (RHD) code CO5BOLD. The spectral synthesis on these models is performed with the line synthesis code LINFOR3D.