Atmospheric velocity fields in tepid main sequence stars

TL;DR

This study investigates local atmospheric velocity fields in main sequence stars of types B, A, and F, revealing new signatures in stars with low v sin i and exploring their dependence on stellar parameters, especially effective temperature.

Contribution

It identifies new stars with detectable velocity field signatures and analyzes how these signatures vary with stellar temperature and peculiarity, expanding understanding of stellar atmospheres.

Findings

Velocity fields detected in six new stars.

Signatures are stronger in Am stars.

Velocity signatures linked to stellar temperature below 10000 K.

Abstract

The line profiles of the stars with v sin i below a few km/s can reveal direct signatures of local velocity fields (e.g. convection) in stellar atmospheres. This effect is well established in cool main sequence stars, and has been detected and studied in three A stars. This paper reports observations of main sequence B, A and F stars with two goals: (1) to identify additional stars having sufficiently low values of v sin i to search for spectral line profile signatures of local velocity fields, and (2) to explore how the signatures of the local velocity fields in the atmosphere depend on stellar parameters such as effective temperature T_eff and peculiarity type. For stars having T_eff below about 10000 K, we always detect local atmospheric velocity fields indirectly through a non-zero microturbulence parameter, but not for hotter stars. Among the A and F stars in our sample having the sharpest lines, direct tracers of atmospheric velocity fields are found in six new stars. The velocity field signatures identified include asymmetric excess line wing absorption, deeper in the blue line wing than in the red; line profiles of strong lines that are poorly fit by computed profiles; and strong lines that are broader than they should be for the v sin i values deduced from weak lines. These effects are found in both normal and Am stars, but seem stronger in Am stars. These data still have not been satisfactorily explained by models of atmospheric convection, including numerical simulations.