KIC 10449976: Discovery of an extreme helium subdwarf in the Kepler field

Abstract

Optical spectroscopy of the blue star KIC 10449976 shows that it is an extremely heliumrich subdwarf with effective temperature Teff = 40 000 ± 300K and surface gravity log g = 5.3 ± 0.1. Radial-velocity measurements over a 5 d time-scale show an upper variability limit of ≈50 ± 20 km s-1. Kepler photometry of KIC 10449976 in both long and short cadence modes shows evidence for a periodic modulation on a time-scale of ≈3.9 d. We have examined the possibility that this modulation is not astrophysical but conclude that it is most likely real. We discuss whether the modulation could be caused by a low-mass companion, by stellar pulsations or by spots. The identification of any one of these as cause has important consequences for understanding the origin of helium-rich subdwarfs. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.