A Measurement of Stellar Surface Gravity Hidden in Radial Velocity Differences of Co-moving Stars

TL;DR

This paper demonstrates a method to detect stellar surface gravity effects via radial velocity differences in co-moving stars using Gaia data, revealing a significant gravitational redshift signal.

Contribution

It introduces a novel statistical approach leveraging Gaia data to measure gravitational redshift and convective blueshift effects in non-degenerate stars.

Findings

Detected a positive correlation between radial velocity differences and surface gravity.

Null hypothesis rejected at 5 sigma significance level.

Method shows promise for constraining stellar models and mass-luminosity relations.

Abstract

The gravitational redshift induced by stellar surface gravity is notoriously difficult to measure for non-degenerate stars, since its amplitude is small in comparison with the typical Doppler shift induced by stellar radial velocity. In this study, we make use of the large observational data set of the Gaia mission to achieve a significant reduction of noise caused by these random stellar motions. By measuring the differences in velocities between the components of pairs of co-moving stars and wide binaries, we are able to statistically measure the combined effects of gravitational redshift and convective blueshifting of spectral lines, and nullify the effect of the peculiar motions of the stars. For the subset of stars considered in this study, we find a positive correlation between the observed differences in Gaia radial velocities and the differences in surface gravity and convective blueshift inferred from effective temperature and luminosity measurements. The results rule out a null signal at the $5\sigma$ level for our full data-set. Additionally, we study the sub-dominant effects of binary motion, and possible systematic errors in radial velocity measurements within Gaia. Results from the technique presented in this study are expected to improve significantly with data from the next Gaia data release. Such improvements could be used to constrain the mass-luminosity relation and stellar models which predict the magnitude of convective blueshift.