Alex Wallace

Astrometric Detection and Characterisation of Hidden Stellar Companions with Gaia

Since its first data release, the Gaia mission has provided a wealth of knowledge about the precise positions and motions of nearby stars. From this, we can measure parallax and proper motion to high degrees of accuracy. However, if a star is orbited by an unseen companion, the track is slightly distorted leading to a potentially inaccurate calculation of the system’s proper motion and parallax. This discrepancy is quantified by the renormalised unit weight error (RUWE) reported in the Gaia catalogue. The higher the RUWE, the greater the discrepancy. Using Bayesian inference with pystan, we use this error and the fitted track parameters to constrain the nature of a potential binary system using data from Gaia’s DR3. From this, it is possible to calculate the true parallax and proper motion of the system. I apply this method to several examples ranging from brown dwarf companions to main sequence binaries to black holes. Finally, I demonstrate the extra potential this method has when epoch data is released in DR4.