UNC-CH Physics and Astronomy Colloquium

Brad Barlow, High Point University

“Exploring Peculiar Events in Stellar Evolution Using the Enigmatic Hot Subdwarf Stars”

The lesser-known hot subdwarf stars represent one of the least-understood stages of stellar evolution. Theory shows these core helium-fusing, extreme horizontal branch stars likely formed from red giants that were stripped of their outer hydrogen envelopes, due to Roche lobe overflow and common envelope interactions with a nearby companion. Observations generally support this idea as nearly all hot subdwarfs appear to be in binaries. These systems have surprisingly important roles to play in our understanding of several astrophysical phenomena. Some of the shortest-period binaries are candidate progenitor systems for underluminous Type Iax supernovae and might serve as verification sources for gravitational wave observatories like LISA. Other short-period systems contain brown dwarf companions, suggesting substellar objects might be able to survive red giant engulfment. On the opposite end of the spectrum are the wide hot subdwarf binaries, which have orbital periods from 1-3 years and F/G/K main sequence companions. Surprisingly, many of these systems show significant eccentricity, contrary to the predictions of Roche lobe overflow models. Here I will give a brief introduction to hot subdwarfs and discuss ways in which we exploit their formation histories to improve our understanding of broader areas within astrophysics.