The history of the inner Milky Way: Variable stars across the Galactic Bulge and Nuclear Stellar Disc

Variable stars are precision tools for decoding the formation and evolution of the Milky Way's bar/bulge. Not only do variable stars often follow tight period-luminosity relations enabling accurate 3D mapping, but their pulsations are often related to intrinsic properties such as age and metallicity. For instance, the asymmetry of RR Lyrae light curves is often related to their metallicity, whilst the periods of Mira variable stars are believed to be related to their age. From this information we can begin to disentangle the sequence of events that formed the Milky Way's bar/bulge.

I describe searches for variable stars across the Galactic bulge and the nuclear stellar disc using the VISTA Variables in the Via Lactea (VVV) survey. The first of these is a targeted search for Mira variable stars within the nuclear stellar disc. ~1800 Mira variables have been discovered from which variation of proper motion dispersion with period suggests the bar formed ~8-10 Gyr ago. The second approach is a supervised classification of 490 million light curves from which ~40000 high-confidence RR Lyrae ab have been found. I will describe ongoing efforts to model the joint kinematic-metallicity distribution of this population for deciphering the early formation history of the bar-bulge.