K2 observations of five pulsating subdwarf-B stars with white dwarf companions

Abstract

We report seismic analyses of five pulsating subdwarf B (sdBV) stars observed during Kepler's K2 mission, each with a white dwarf companion. We find three of the five to be g-mode-dominated hybrid pulsators. For the other two, we only detect g modes. We determine rotation periods from frequency multiplets for four stars and each rotates subsynchronously to its binary period, including PG 0101039 and PG 0902124 both with binary periods near 0.57 d and spin periods near 9 d. We detect frequency multiplets in both p and g modes for PG 0101039 and LT Cnc and determine that PG 0101039 rotates like a solid body while LT Cnc rotates differentially radially with the envelope spinning faster than deeper layers. Mostly, we find these five stars to be quite similar to one another, spectroscopically and seismically. We find the p modes of the three hybrid pulsators to have gaps between regions of power, which we interpret as overtones and apply a technique to assign modes. We examine their g-mode period spacings and deviations thereof and again, find the stars to be similar with period spacings near the average of 250 s and deviations mostly under 25 s. We compare Kepler-observed sdBV stars of different binary types and likely-single pulsators.

Department(s)

Physics, Astronomy, and Materials Science

Document Type

Article

DOI

10.1093/mnras/staf917

Keywords

binaries: close, stars: horizontal branch, Stars: oscillations, subdwarfs

Publication Date

7-1-2025

Journal Title

Monthly Notices of the Royal Astronomical Society

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