Wednesday

I describe two Milky Way research projects that would benefit from fairly rapid identification of high amplitude variability, to enable follow up on a timescale of days to weeks. The first is the case of the vanishing giant stars: three recent cases of very deep and slow eclipses of late type giant stars have been identified so far in the VVV survey (VVV-WIT-08, VVV-WIT-10, VVV-WIT-11). The first, VVV-WIT-08, was analysed in detail in a recently accepted paper (L. C. Smith et al.) with the help of OGLE optical data. In the last, VVV-WIT-11, the giant star dropped below the detection limit for an entire observing season. These three discoveries add to another two in the literature involving M-type giants (TYC2505-672-1 and the ongoing ASASSN-21co event), suggesting that there is a broad class of wide binary systems wherein a late-type giant star is eclipsed by a circumsecondary disc. The evolutionary pathway(s) are yet to be determined. The second project is the ongoing work on eruptive variable YSOs in the infrared and the visible. Here, the YSOs rise dramatically in brightness on a timescale ranging from a few weeks to a few years, due to an accretion disc instability whose nature is not yet determined. Rapid identification of both types of event would enable fast photometric and spectroscopic follow up to help solve the nature of the secondary companions to the giant stars, and probe the nature of the YSO disc instability as it proceeds.