EPIC 211779126: a rare hybrid pulsating subdwarf B star richly pulsating in both pressure and gravity modes

Author： Baran A. S. Reed M. D. Østensen R. H. Telting J. H. Jeffery C. S.

E-ISSN： 1432-0746|597|issue|A95-A95

ISSN： 0004-6361

Source： Astronomy & Astrophysics, Vol.597, Iss.issue, 2017-01, pp. : A95-A95

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Abstract

We present our analysis of EPIC 211779126, a pulsating subdwarf B star discovered with the Kepler spacecraft during K2 Campaign 5. We found 154 frequencies in the g-mode region as well as 29 frequencies in the p-mode region. This makes EPIC 211779126 a rare hybrid pulsator with a rich pulsation spectrum in both regions. We successfully identified modal degrees and relative radial orders of most of the g-modes using asymptotic period spacing, and modal degrees of some of the p-modes using rotational splitting. We detected trapped modes, which are a very important feature for constraining theoretical models. Our ground-based spectroscopic observations revealed no companion, therefore EPIC 211779126 is likely a single sdB star. Using p-mode multiplets, we derived a rotation period of approximately 16 days, making EPIC 211779126 the fastest rotating non-binary subdwarf B pulsator observed with Kepler. However, we do not find any resolved multiplets among the high-amplitude g-mode pulsations that correspond to the rotation rate inferred from the p-mode splittings. This may indicate that the star’s core is rotating more slowly than its envelope.