A pulsation zoo in the hot subdwarf B star KIC 10139564 observed by Kepler

Abstract

We present our analyses of 15 months of Kepler data on KIC 10139564. We detected 57 periodicities with a variety of properties not previously observed all together in one pulsating subdwarf B (sdB) star. Ten of the periodicities were found in the low-frequency region, and we associate them with nonradial g modes. The other periodicities were found in the highfrequency region, which are likely p modes. We discovered that most of the periodicities are components of multiplets with a common spacing. Assuming that multiplets are caused by rotation, we derive a rotation period of 25.6 ± 1.8 d. The multiplets also allow us to identify the pulsations to an unprecedented extent for this class of pulsator. We also detect l ≥ 2 multiplets, which are sensitive to the pulsation inclination and can constrain limb darkening via geometric cancellation factors. While most periodicities are stable, we detected several regions that show complex patterns. Detailed analyses showed that these regions are complicated by several factors. Two are combination frequencies that originate in the super-Nyquist region and were found to be reflected below the Nyquist frequency. The Fourier peaks are clear in the super-Nyquist region, but the orbital motion of Kepler smears the Nyquist frequency in the barycentric reference frame and this effect is passed on to the sub-Nyquist reflections. Others are likely multiplets but unstable in amplitudes and/or frequencies. The density of periodicities also makes KIC 10139564 challenging to explain using published models. This menagerie of properties should provide tight constraints on structural models, making this sdB star the most promising for applying asteroseismology.To support our photometric analysis, we have obtained spectroscopic radial-velocity measurements of KIC 10139564 using low-resolution spectra in the Balmer-line region. We did not find any radial-velocity variation. We used our high signal-to-noise average Based also on observations made with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway and Sweden, in the Spanish Observatorio del Roque de los Muchachos

The blue-edge problem of the V1093 Herculis instability strip revisited using evolutionary models with atomic diffusion

“…Baran et al 2011) and that p-mode pulsator KIC 10139564 also shows g-mode pulsations while it has an effective temperature that is close to 32 000 K (Baran et al 2012, indicated with a black point on Fig. 5).…”

“…The black point indicates KIC 10139564 (Baran et al 2012), which is a hybrid pulsator that predominantly shows p-mode pulsations. The vertical dashed lines indicate the blue edges of the instability strips predicted by Jeffery & Saio (2006) and Hu et al (2009). hybrid pulsators that show both p-and g-mode pulsations in red.…”

Keplerdetection of a new extreme planetary system orbiting the subdwarf-B pulsator KIC 10001893

“…Indeed we do not see any signature of a magnetic field in our optical spectra or in the pulsation spectrum. Moreover, sdB stars have relatively long rotational periods, P ROT > 1 day from spectroscopy (Geier & Heber 2012), while values up to ∼40 days are obtained from pulsation rotational splitting (e.g., Baran et al 2012). This rules out all (known) alternatives other than orbitally driven modulations.…”

“…With a Kepler magnitude of 15.85, KIC 10001893 is one out of 19 subdwarf B (sdB) pulsators observed by the Kepler spacecraft in its primary mission , 2011, 2012Kawaler et al 2010a,b;Reed et al 2010Reed et al , 2011Reed et al , 2012Van Grootel et al 2010;Baran et al 2011Baran et al , 2012Charpinet et al 2011b). The spectroscopic atmospheric parameters of KIC 10001893, T eff = 26 700 ± 300 K, log g = 5.30 ± 0.04, and log (N He /N H ) = −2.09±0.1 are very compatible with the g-mode instability strip (Østensen et al 2011).…”

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

“…In addition, rotationally split multiplets have been used to identify the and m modes of pulsations [e.g. 6,7]. Stellar rotation lifts the frequency degeneracy and gives rise to frequency multiplets whose splittings follow the relation ∆ν = ∆mΩ(1 − C n, ).…”