Kepler observations of variability in B-type stars

TL;DR

This study analyzes Kepler light curves of 48 B-type stars, revealing diverse pulsation behaviors, non-pulsators within instability strips, and potential rotation-related phenomena, challenging ground-based observations and theoretical models.

Contribution

It provides the first detailed Kepler-based analysis of B-type star variability, highlighting differences from ground observations and identifying new variability patterns.

Findings

Most low frequencies are high-degree modes predicted to be unstable.

Presence of non-pulsating stars within instability strips.

Detection of frequency groupings possibly related to rotation.

Abstract

The analysis of the light curves of 48 B-type stars observed by Kepler is presented. Among these are 15 pulsating stars, all of which show low frequencies characteristic of SPB stars. Seven of these stars also show a few weak, isolated high frequencies and they could be considered as SPB/beta Cep hybrids. In all cases the frequency spectra are quite different from what is seen from ground-based observations. We suggest that this is because most of the low frequencies are modes of high degree which are predicted to be unstable in models of mid-B stars. We find that there are non-pulsating stars within the beta Cep and SPB instability strips. Apart from the pulsating stars, we can identify stars with frequency groupings similar to what is seen in Be stars but which are not Be stars. The origin of the groupings is not clear, but may be related to rotation. We find periodic variations in other stars which we attribute to proximity effects in binary systems or possibly rotational modulation. We find no evidence for pulsating stars between the cool edge of the SPB and the hot edge of the delta Sct instability strips. None of the stars show the broad features which can be attributed to stochastically-excited modes as recently proposed. Among our sample of B stars are two chemically peculiar stars, one of which is a HgMn star showing rotational modulation in the light curve.