Modelling linewidths of Kepler red giants in NGC 6819

TL;DR

This study compares theoretical damping rates with Kepler-observed linewidths of red-giant stars in NGC 6819, demonstrating good agreement and highlighting the importance of calibrated convection models for asteroseismology.

Contribution

It introduces a detailed modeling approach using 3D simulation-calibrated convection profiles to accurately reproduce observed linewidths in red giants.

Findings

Modelled damping rates match Kepler observations well.

Characteristic depression in linewidths around maximum oscillation frequency is reproduced.

Sensitivity analysis shows robustness of damping rates to convection model parameters.

Abstract

We present a comparison between theoretical, frequency-dependent, damping rates and linewidths of radial-mode oscillations in red-giant stars located in the open cluster NGC 6819. The calculations adopt a time-dependent non-local convection model, with the turbulent pressure profile being calibrated to results of 3D hydrodynamical simulations of stellar atmospheres. The linewidths are obtained from extensive peakbagging of Kepler lightcurves. These observational results are of unprecedented quality owing to the long continuous observations by Kepler. The uniqueness of the Kepler mission also means that, for asteroseismic properties, this is the best data that will be available for a long time to come. We therefore take great care in modelling nine RGB stars in NGC 6819 using information from 3D simulations to obtain realistic temperature stratifications and calibrated turbulent pressure profiles. Our modelled damping rates reproduce well the Kepler observations, including the characteristic depression in the linewidths around the frequency of maximum oscillation power. Furthermore, we thoroughly test the sensitivity of the calculated damping rates to changes in the parameters of the nonlocal convection model.