C.S. Jeffery, G. Ramsay, N. Naslim, R. Carrera, S. Greiss, T. Barclay, R. Karjalainen, A. Brooks, P. Hakala

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

Figure 3. The normalised WHT optical spectrum of KIC 10449976 fitted with the model described in §3 optimized for abundances of C, N, Si and Ne, together with line identifications.

Abstract

Optical spectroscopy of the blue star KIC 10449976 shows that it is an extremely helium-rich subdwarf with effective temperature Teff = 40 000 ± 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−1. 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.

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Last Revised: 2012 December 6th