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
We present results from the first two quarters of a survey to search for pulsations in compact stellar objects with the Kepler spacecraft. The survey sample and the various methods applied in its compilation are described, and spectroscopic observations are presented to separate the objects into accurate classes. From the Kepler photometry we clearly identify nine compact pulsators and a number of interesting binary stars. Of the pulsators, one shows the strong, rapid pulsations typical of a V361 Hya‐type sdB variable (sdBV); seven show long‐period pulsation characteristics of V1093 Her‐type sdBVs; and one shows low‐amplitude pulsations with both short and long periods. We derive effective temperatures and surface gravities for all the subdwarf B stars in the sample and demonstrate that below the boundary region where hybrid sdB pulsators are found, all our targets are pulsating. For the stars hotter than this boundary temperature a low fraction of strong pulsators (<10 per cent) is confirmed. Interestingly, the short‐period pulsator also shows a low‐amplitude mode in the long‐period region, and several of the V1093 Her pulsators show low‐amplitude modes in the short‐period region, indicating that hybrid behaviour may be common in these stars, also outside the boundary temperature region where hybrid pulsators have hitherto been found.
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