Physics 003

Title:

High-Speed Photometry of New Variable Hot Subdwarfs from Gaia eDR3

Abstract:

Hot subdwarf stars are the exposed helium-fusing cores of giant stars that result from prior interaction with a binary companion. On the Hertzprung-Russel diagram, they sit below the main-sequence and at the blue end of the horizontal branch. In this talk, I will present a search for new variable hot subdwarfs in Gaia eDR3 using the Zwicky Transient Facility and the 2.1 m Otto Struve telescope at McDonald Observatory. Priority for follow-up observations was based on location on the HR diagram and on a variability metric determined from the empirically determined Gaia flux uncertainties. I will also present a simple method for exploiting the Gaia flux uncertainties to estimate stellar variability, which is an an extremely useful tool for finding new variable stars when observing resources are limited. Notable discoveries from this search include a 72-minute ellipsoidally modulated hot subdwarf + white dwarf binary and a 67-minute HW Vir system (a special class of eclipsing hot subdwarf binaries), which is the shortest period HW Vir discovered to date. This short-period system may enable the opportunity to place constraints on formation theory of hot subdwarfs by addressing questions on the masses of objects able to survive the common envelope phase and on the minimum companion mass needed to eject a common envelope.