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

TL;DR

This paper reports the discovery of an extremely helium-rich subdwarf star in the Kepler field, characterized by high temperature, specific gravity, and periodic brightness modulation, with implications for understanding helium-rich subdwarfs.

Contribution

It presents the first detailed characterization of an extreme-helium subdwarf in the Kepler field, including its spectral properties and potential causes of brightness modulation.

Findings

Star is an extremely helium-rich subdwarf with T=40000K

Detected a ~3.9-day periodic brightness modulation

Possible causes include a low-mass companion, pulsations, or spots

Abstract

Optical spectroscopy of the blue star KIC 10449976 shows that it is an extremely helium-rich subdwarf with effective temperature T=40000+/-300 K and surface gravity log g=5.3+/-0.1. Radial-velocity measurements over a five-day timescale show an upper variability limit of ~50+/-20 km/s. Kepler photometry of KIC 10449976 in both long and short cadence modes shows evidence for a periodic modulation on a timescale of ~3.9 days. We have examined the possibility that this modulation is not astrophysical but conclude 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.