Speaker
Description
Metal-rich RR Lyrae stars in the Milky Way disc challenge their classical interpretation as purely old tracers. Binary evolution has been proposed as a viable formation channel, predicting a significant population of long-period RR Lyrae binaries. However, none have been robustly identified so far, including in Gaia DR3.
In this talk, I show that Gaia DR3 non-detections already point to a tension with current binary-formation models, but do not yet provide a definitive test. Using a carefully selected sample of Gaia RR Lyrae stars and realistic simulations of Gaia astrometry, we find that intrinsic stellar variability strongly suppresses binary detectability, substantially weakening constraints on the binary fraction. As a result, while the data disfavour the highest binary fractions predicted by some models, firm conclusions cannot yet be drawn.
Gaia DR4, together with an explicit treatment of stellar variability, will be crucial to resolving this tension.
