Signatures of Granulation in the Spectra of K-Dwarfs

TL;DR

This study uses high-resolution spectra of K-dwarfs to observe granulation effects caused by convection, compares them with 3D models, and finds minimal impact on iron abundance measurements.

Contribution

First detailed comparison of high-resolution K-dwarf spectra with 3D hydrodynamical models to validate granulation effects and their influence on stellar abundance analysis.

Findings

Line bisectors and shifts are about 200 m/s, detectable with careful observations.

3D models agree reasonably with observed line profiles.

3D-LTE effects have negligible impact on iron abundance determinations.

Abstract

Very high resolution (R>150,000) spectra of a small sample of nearby K-dwarfs have been acquired to measure the line asymmetries and central wavelength shifts caused by convective motions present in stellar photospheres. This phenomenon of granulation is modeled by 3D hydrodynamical simulations but they need to be confronted with accurate observations to test their realism before they are used in stellar abundance studies. We find that the line profiles computed with a 3D model agree reasonably well with the observations. The line bisectors and central wavelength shifts on K-dwarf spectra have a maximum amplitude of only about 200 m/s and we have been able to resolve these granulation effects with a very careful observing strategy. By computing a number of iron lines with 1D and 3D models (assuming local thermodynamic equilibrium), we find that the impact of 3D-LTE effects on classical iron abundance determinations is negligible.