First Kepler results on compact pulsators VII. Pulsating subdwarf B stars detected in the second half of the survey phase

TL;DR

This paper reports the discovery and analysis of five new pulsating subdwarf B stars from Kepler data, revealing their g-mode pulsation characteristics, mode spacings, and potential hybrid nature, completing the survey of compact pulsators.

Contribution

The study provides detailed pulsation spectra of five new sdB stars, identifying their mode patterns and confirming the survey's completeness in detecting compact pulsators.

Findings

All five stars are multiperiodic g-mode pulsators.

Average period spacings suggest l=1 and 2 modes.

Most stars are V1093 Her type, with some showing hybrid features.

Abstract

We present five new pulsating subdwarf B (sdB) stars discovered by the Kepler spacecraft during the asteroseismology survey phase. We perform time-series analysis on the nearly continuous month-long Kepler datasets of these 5 objects; these datasets provide nearly alias-free time-series photometry at unprecedented precision. Following an iterative prewhitening process we derive the pulsational frequency spectra of these stars, separating out artefacts of known instrumental origin. We find that these new pulsating sdB stars are multiperiodic long-period pulsators of the V1093 Her type, with the number of periodicities ranging from 8 (KIC8302197) to 53 (KIC11558725). The frequencies and amplitudes are typical of g-mode pulsators of this type. We do not find any evidence for binarity in the five stars from their observed pulsation frequencies. As these are g-mode pulsators, we briefly looked for period spacings for mode identification, and found average spacings about 260s and 145s. This may indicate l=1 and 2 patterns. Some modes may show evidence of rotational splitting. These discoveries complete the list of compact pulsators found in the survey phase. Of the 13 compact pulsators, only one star was identified as a short-period (p-mode) V361Hya pulsator, while all other new pulsators turned out to be V1093 Her class objects. Among the latter objects, two of them seemed to be pure V1093 Her while the others show additional low amplitude peaks in the p-mode frequency range, suggesting their hybrid nature. Authenticity of these peaks will be tested with longer runs currently under analysis.