White dwarf period tables – I. Pulsators with hydrogen-dominated atmospheres

We collected all known white dwarf pulsators with hydrogen-dominated atmospheres and list their main photometric and atmospheric parameters together with their pulsation periods and amplitudes observed at different epochs. Exploring the pulsating white dwarf related literature with the systematic use of the SIMBAD and the NASA’s Astrophysics Data System (ADS) databases. Four tables listing seven ZZ Ceti stars in detached white dwarf plus main-sequence binaries, seven extremely low-mass DA pulsators, three hot DAVs and 180 ZZ Ceti stars

KIC 9533489: a genuine γ Doradus – δ Scuti Kepler hybrid pulsator with transit events

Context Several hundred candidate hybrid pulsators of type A–F have been identified from space-based observations. Their large number allows both statistical analyses and detailed investigations of individual stars. This offers the opportunity to study the full interior of the genuine hybrids, in which both low-radial-order p- and high-order g-modes are self-excited at the same time. However, a few other physical processes can also be responsible for the observed hybrid nature, related to binarity or to surface inhomogeneities. The finding that most δ Scuti stars also show long-period light variations represents a real challenge for theory. Aims We aim at determining the pulsation frequencies of KIC 9533489, to search for regular patterns and spacings among them, and to investigate the stability of the frequencies and the amplitudes. An additional goal is to study the serendipitously detected transit events: is KIC 9533489 the host star? What are the limitations on the physical parameters of the involved bodies? Methods Fourier analysis of all the available Kepler light curves. Investigation of the frequency and period spacings. Determination of the stellar physical parameters from spectroscopic observations. Modelling of the transit events. Results The Fourier analysis of the Kepler light curves revealed 55 significant frequencies clustered into two groups, which are separated by a gap between 15 and 27 d −1. The light variations are dominated by the beating of two dominant frequencies located at around 4 d −1 . The amplitudes of these two frequencies show a monotonic long-term trend. The frequency spacing analysis revealed two possibilities: the pulsator is either a highly inclined moderate rotator (v ≈ 70 km s −1 , i > 70 ◦ ) or a fast rotator (v ≈ 200 km s −1 ) with i ≈ 20 ◦ . The transit analysis disclosed that the transit events, which occur with a ≈ 197 d period may be caused by a 1.6 R_Jup body orbiting a fainter star, which would be spatially coincident with KIC 9533489

Orbital and physical properties of the σ Ori Aa,Ab,B triple system

We provide a complete characterization of the astrophysical properties of the σ Ori Aa,Ab,B hierarchical triple system, and an improved set of orbital parameters for the highly eccentric σ Ori Aa,Ab spectroscopic binary. We compiled a spectroscopic dataset comprising 90 high-resolution spectra covering a total time span of 1963 days. We applied the Lehman-Filh ́es method for a detailed orbital analysis of the radial velocity curves and performed a combined quantitative spectroscopic analysis of the σ Ori Aa,Ab,B system by means of the stellar atmosphere code fastwind. We used our own plus other available information on photometry and distance to the system for measuring the radii, luminosities, and spectroscopic masses of the three components. We also inferred evolutionary masses and stellar ages using the Bayesian code bonnsai. The orbital analysis of the new radial velocity curves led to a very accurate orbital solution of the σ Ori Aa,Ab pair. We provided indirect arguments indicating that σ Ori B is a fast rotating early-B dwarf. The fastwind+bonnsai analysis showed that the Aa,Ab pair contains the hottest and most massive components of the triple system while σ Ori B is a bit cooler and less massive. The derived stellar ages of the inner pair are intriguingly younger than the one widely accepted for the σ Orionis cluster, at 3 ± 1 Ma. The outcome of this study will be of key importance for a precise determination of the distance to the σ Orionis cluster, the interpretation of the strong X-ray emission detected for σ Ori Aa,Ab,B, and the investigation of the formation and evolution of multiple massive stellar systems and substellar objects

KIC 2831097. A short orbital-period candidate RR Lyrae binary

KIC 2831097 was discovered to be a first-overtone RR Lyrae pulsator based on 4-year Kepler photometry (Sódor et al. 2017, MNRAS, 465, L1). The data show strong, 0.1 d amplitude systematic phase variations that can be explained by light travel-time effect caused by an about 2-year period orbital motion in a binary system, superimposed on a linear pulsation-period decrease. To verify the binary hypothesis, several well-timed radial-velocity observations will be sufficient

MOST light-curve analysis of the gamma Dor pulsator HR 8799, showing resonances and amplitude variations

Context The central star of the HR 8799 system is a gamma Doradus-type pulsator. The system harbours four planetary-mass companions detected by direct imaging, and is a good solar system analogue. The masses of the companions are not known accurately, because the estimation depends strongly on the age of the system, which is also not known with sufficient accuracy. Asteroseismic studies of the star might help to better constrain the age of HR\,8799. We organized an extensive photometric and multi-site spectroscopic observing campaign for studying the pulsations of the central star. Aims The aim of the present study is to investigate the pulsation properties of HR 8799 in detail via the ultra-precise 47-d-long nearly continuous photometry obtained with the MOST space telescope, and to find as many independent pulsation modes as possible, which is the prerequisite of an asteroseismic age determination. Methods We carried out Fourier analysis of the wide-band photometric time series. Results e find that resonance and sudden amplitude changes characterize the pulsation of HR 8799. The dominant frequency is always at f_1 = 1.978 d^-1. Many multiples of one ninth of the dominant frequency appear in the Fourier spectrum of the MOST data: n/9 f_1, where n = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 13, 14, 17, 18\}. Our analysis also reveals that many of these peaks show strong amplitude decrease and phase variations even on the 47-d time-scale. The dependencies between the pulsation frequencies of HR 8799 make the planned subsequent asteroseismic analysis rather difficult. We point out some resemblance between the light curve of HR 8799 and the modulated pulsation light curves of Blazhko RR Lyrae stars

Photometric and Spectroscopic Investigations of the Galactic Field RRc Candidates V764 Mon and HY Com

By analyzing photometric and spectroscopic time series, we show that the pulsator V764 Mon, assumed to be the brightest RR Lyr star in the sky, is in fact a rapidly rotating δ Sct star with an unusually long dominant period (P1=0.29 d). Our spectroscopy confirmed the binarity of V764 Mon discovered by the Gaia satellite. In the case of HY Com, a bona fide RRc star, we present its first complete radial velocity curve. Additionally, we found that the star continues its strong phase variation reported before

Spectroscopic and photometric time series of the bright RRc star T Sex

We present spectroscopic time series observations on one of the brightest northern RRc stars, namely T Sex. Additionally, we also analysed extended photometric data sets, particularly the recent observations of the TESS space telescope. The main findings of our studies are as follows: T Sex, unlike all RRc stars whose space photometry has been analysed, shows only the 0.5fx frequency as an additional pulsation frequency. With this, T Sex may be the first represent of such rare RRc stars found from space photometry. The spectroscopic data show a periodic distortion of the H α line with the pulsation phase. This phenomenon has not been reported for any RR Lyrae stars. The characteristic line distortion is probably caused by the turbulent convection, which resulted in higher macroturbulent velocity for T Sex than that for typical RRab stars. Line doubling of the Na D line was observed between the 0.37 and 0.80 pulsation phases. The explanation of this phenomenon is that the two absorption components originate from different sources. The redder component comes from the pulsating atmosphere of the star, while the bluer one comes from the interstellar space. At phase 0.438, we detected emission on the Na D line, which may indicate a weak shock wave