Surface convection: from the Sun to red giant stars

TL;DR

This paper examines how surface convection length scales differ between the Sun and red giant stars, using observational data and theoretical models to assess the applicability of solar-calibrated parameters.

Contribution

It demonstrates that the solar-calibrated convective length scale does not accurately describe surface convection in red giant stars, highlighting the need for revised models.

Findings

Solar-calibrated convective length scale fails for red giants

Observational data shows different surface convection characteristics in red giants

Models need adjustment to account for different stellar surface conditions

Abstract

We check how the change in surface conditions between the Sun and red giant branch stars changes the characteristic surface convection length scale to be used in models. We investigate the question in the case of the mixing length theory and of the phenomenology of full spectrum of turbulence. For the observational part, we rely on independent measurements of effective temperatures and interferometric radii of nearby red giants. We find that the local red giant branch cannot be explained taking into account the solar calibrated convective length scale.