A Non-Detection of Red Supergiant Convection in Gaia

TL;DR

This study investigates whether Gaia can detect surface convection in red supergiants through photocenter shifts, but finds the expected signals are too small compared to Gaia's noise levels.

Contribution

The paper provides the first observational test of Gaia's ability to detect red supergiant convection via photocenter motions, finding no detectable signal.

Findings

Gaia's astrometric noise is too large to detect RSG convection signals.

RSGs show similar excess noise as other stars of comparable brightness.

Photocenter shifts due to convection are below Gaia's detection threshold.

Abstract

Large scale surface convection on red supergiants (RSGs) can lead to shifts in the photocenter of the star which might be measured by Gaia and used as a new probe of the surface dynamics of these rare but important stars. Unlike brightness variations, photocenter motions would provide information on the physical scale of the convective cells. The signal would be that RSGs show an excess astrometric noise at the level of a few percent of the stellar radius. Unfortunately, we find that the excess astrometric noise level of Gaia EDR3 is roughly an order of magnitude too large to detect the predicted motions and that RSGs have excess astrometric noise indistinguishable from other stars of similar magnitude and parallax. The typical excess astrometric noise steadily decreases with G magnitude (for G<11 mag), so it is crucial to compare stars of similar brightness.