First Kepler results on compact pulsators - VI. Targets in the final half of the survey phase

Abstract

We present results from the final 6 months of a survey to search for pulsations in white dwarfs (WDs) and hot subdwarf stars with the Kepler spacecraft. Spectroscopic observations are used to separate the objects into accurate classes, and we explore the physical parameters of the subdwarf B (sdB) stars and white dwarfs in the sample. From the Kepler photometry and our spectroscopic data, we find that the sample contains five new pulsators of the V1093 Her type, one AM CVn type cataclysmic variable and a number of other binary systems.This completes the survey for compact pulsators with Kepler. No V361 Hya type of shortperiod pulsating sdB stars were found in this half, leaving us with a total of one single multiperiodic V361 Hya and 13 V1093 Her pulsators for the full survey. Except for the sdB pulsators, no other clearly pulsating hot subdwarfs or white dwarfs were found, although a few

Hot subluminous stars: Highlights from the MUCHFUSS andKeplermissions

“…Amongst the sixteen sdB stars cooler than 28 000 K in the Kepler sample, twelve stars (75%) showed V1093 Her type pulsation, the fraction being in agreement with expectations from ground-based studies. [12] conclude that "thanks to the exceptional precision of the Kepler measurements, we can now conclude that there certainly are sdB stars, both on the hot and on the cold ends of the EHB, that show no trace of pulsations.…”

“…The initial interest of sdB stars in the Kepler field was to study their oscillations [12]. Two classes of such multimode, low-amplitude pulsators are known: the short-period V361 Hya stars (P≈120-600 s) and the V1093 Her stars (P ≈ 45-120 min).…”

“…During the first year of the Kepler mission, thirty-two sdB pulsator candidates hotter than 28 000 K have been surveyed [12] and only one was found to be an unambiguous V361 Hya pulsator. Amongst the sixteen sdB stars cooler than 28 000 K in the Kepler sample, twelve stars (75%) showed V1093 Her type pulsation, the fraction being in agreement with expectations from ground-based studies.…”

Planetary systems and real planetary nebulae from planet destruction near white dwarfs

“…The respective orbital periods of the planets they have found are P 1 = 5.273 hours, P 2 = 7.807 hours, and P 3 = 19.48 hours. This star is an extreme horizontal branch (EHB) star that burns helium in its core and contains a very little envelope mass (Baran et al 2011;Østensen et al 2011). Spectroscopically, EHB stars are classified as hot subdwarf (sdB or sdO) stars.…”

Pulsations in hot subdwarf stars: recent advances and prospects for testing stellar physics

“…Isolated sdB stars, for their part, should not be affected by such effects and their rotation therefore mostly reflects their past history, i.e., the result of the secular evolution of angular momentum in their progenitors. Evidence is growing that these stars are very slow rotators with rotation periods of the order of weeks or even months (Baran et al 2009(Baran et al , 2013Charpinet et al 2011;Foster et al 2015;Peters et al 2016, in preparation). Interestingly, such timescales can be connected to recent results from asteroseismology of red giants clearly indicating that the cores of red clump stars also rotate very slowly, with periods strikingly similar to those inferred for isolated sdB stars (see, e.g., Aerts 2015; Mosser et al 2013 and references therein).…”