Sandra Liss
Astronomy graduate student
A period histogram of 140 sdB binaries with a range of companion types. All of the long period systems (orange marks) have companions of spectral type K4 or earlier. See arXiv:1208.4359.
Hot Subdwarf Binaries
Hot subdwarf B (sdB) stars are core helium burning stars that were somehow stripped of most of their hydrogen envelopes while on the red giant branch. A large fraction of these stars show composite spectra indicative of cool main sequence companions, and binary population synthesis models suggest that these systems should have short periods (P < 10 days). However, radial velocity surveys have failed to find variations on these short time scales.
At Penn State, I worked with Richard Wade and Brad Barlow on a long-term radial velocity study of sdBs with cool main sequence companions. Using spectra obtained using the Medium and High Resolution Spectrographs on the Hobby-Eberly Telescope, we determined the orbital parameters of 15 sdB+cool companion systems. We found that each system has an orbital period on the order of 1 to 3 years and that many of these systems appear to to have non-circular orbits. Both of these findings contradict the leading theories of sdB formation, and suggest that such theories need to be revisited.