Teff and logg dependence of FeH in M-dwarfs

TL;DR

This study uses 3D radiative-hydrodynamic models to analyze FeH spectral features in M-dwarfs, aiming to distinguish between broadening mechanisms and assess the necessity of 3D modeling for accurate stellar characterization.

Contribution

It provides a detailed analysis of FeH line dependence on gravity and temperature in M-dwarfs using 3D models, highlighting when 3D atmospheres are necessary for spectral interpretation.

Findings

FeH line strength varies with gravity and temperature.

Line width correlates with velocity fields and gravity.

FeH lines can help measure stellar parameters in M-dwarfs.

Abstract

We present synthetic FeH band spectra in the z-filter range for several M-dwarf models with logg=3.0-5.0 [cgs] and Teff=2800K -3450K. Our aim is to characterize convective velocities in M-dwarfs and to give a rough estimate of the range in which 3D-atmosphere treatment is necessary and where 1D-atmosphere models suffice for the interpretation of molecular spectral features. This is also important in order to distinguish between the velocity-broadening and the rotational- or Zeeman-broadening. The synthetic spectra were calculated using 3D CO5BOLD radiative-hydrodynamic (RHD) models and the line synthesis code LINFOR3D. We used complete 3D-models and high resolution 3D spectral synthesis for the detailed study of some well isolated FeH lines. The FeH line strength shows a dependence on surface gravity and effective temperature and could be employed to measure both quantities in M-type objects. The line width is related to the velocity-field in the model stars, which depends strongly on surface gravity. Furthermore, we investigate the velocity-field in the 3D M-dwarf models together with the related micro- and macro-turbulent velocities in the 1D case. We also search for effects on the lineshapes.