First Kepler results on compact pulsators - VIII. Mode identifications via period spacings in g-mode pulsating subdwarf B stars

Abstract

We investigate the possibility of nearly equally spaced periods in 13 hot subdwarf B (sdB) stars observed with the Kepler spacecraft and one observed with CoRoT. Asymptotic limits for gravity (g-)mode pulsations provide relationships between equal-period spacings of modes with differing degrees and relationships between periods of the same radial order n but differing degrees . Period transforms, Kolmogorov-Smirnov tests and linear least-squares fits have been used to detect and determine the significance of equal-period spacings. We have also used Monte Carlo simulations to estimate the likelihood that the detected spacings could be produced randomly.Period transforms for nine of the Kepler stars indicate = 1 period spacings, with five also showing peaks for = 2 modes. 12 stars indicate = 1 modes using the Kolmogorov-Smirnov test while another shows solely = 2 modes. Monte Carlo results indicate that equal-period spacings are significant in 10 stars above 99 per cent confidence, and 13 of the 14 are above 94 per cent confidence. For 12 stars, the various methods find consistent period spacings to within the errors, two others show some inconsistencies, likely caused by binarity, and the last has significant detections but the mode assignment disagrees between the methods.We use asymptotic period spacing relationships to associate observed periods of variability with pulsation modes for = 1 and 2. From the Kepler first-year survey sample of 13 multiperiodic g-mode pulsators, five stars have several consecutive overtones making period spacings easy to detect, six others have fewer consecutive overtones but period spacings are readily detected, and two stars show marginal indications of equal-period spacings. We also

An Analysis of Pulsating Subdwarf B Star EPIC 203948264 Observed During Campaign 2 ofK2

“…The result of the KS test revealed two common spacings: 260 s and 150 s. We pick out periods with these separations, assign relative overtones, n, and then do a linear regression fit. The solutions, 261.34 ± 0.78 for the = 1 and 151.18 ± 0.34 s for the = 2 sequence agree with asymptotic theory, =2 = =1 / √ 3 [8], and are in agreement with other Kepler-observed g−mode pulsators [5]. Using asymptotic period spacings we identified all but one of the pulsations as = 1 or = 2, with four of them matching both sequences.…”

“…Their periods range from 1660 to nearly 9900 s (101µ to 602µ Hz). Asymptotic period spacings have been detected in all Kepler-observed sdB g−mode pulsators [5] and they all showed similar spacings of around 250 s for the = 1 sequence and 145 s for = 2. Once we had our list of detected periods, we started testing for evenly spaced periods using a Kolmogorov-Smirnov (KS) test.…”

“…Our goal for EPIC 203948264 was to identify the modes of the detected pulsations using asymptotic period spacings and rotationally induced frequency multiplets. Reed et al discovered that sdB stars exhibit asymptotic period spacings in the g−mode region, with the = 1 sequence equally spaced by about 250 s [5]. In addition, rotationally split multiplets have been used to identify the and m modes of pulsations [e.g.…”

Detecting non-uniform period spacings in theKeplerphotometry ofγDoradus stars: methodology and case studies

“…Degroote et al 2010;Savonije 2013;Pápics et al 2014), sdB stars (e.g. Reed et al 2011), subgiants and red giants (e.g. Beck et al 2011Beck et al , 2012Bedding et al 2011;Mosser et al 2012;Deheuvels et al 2014), thanks to data from the space missions CoRoT (Auvergne et al 2009) and Kepler (Koch et al 2010).…”

Revealing the pulsational properties of the V777 Herculis star KUV 05134+2605 by its long-term monitoring

“…Reed et al 2011), the asymptotic ratio of the period spacings of = 1 and 2 modes is ΔΠ l=1 /ΔΠ l=2 = √ 3 = 1.73. For the second fits presented above, this ratio is (31.4 ± 0.3)/(18.0 ± 0.3) = 1.74 ± 0.03.…”