A tidally tilted sectoral dipole pulsation mode in the eclipsing binary TIC 63328020

We report the discovery of the third tidally tilted pulsator, TIC 63328020. Observations with the TESS satellite reveal binary eclipses with an orbital period of 1.1057 d, and δ Scuti-type pulsations with a mode frequency of 21.09533 d−1. This pulsation exhibits a septuplet of orbital sidelobes as well as a harmonic quintuplet. Using the oblique pulsator model, the primary oscillation is identified as a sectoral dipole mode with l = 1, |m| = 1. We find the pulsating star to have M1 ≃ 2.5 M⊙, R1 ≃ 3 R⊙, and Teff, 1 ≃ 8000 K, while the secondary has M2 ≃ 1.1 M⊙, R2 ≃ 2 R⊙, and Teff, 2 ≃ 5600 K. Both stars appear to be close to filling their respective Roche lobes. The properties of this binary as well as the tidally tilted pulsations differ from the previous two tidally tilted pulsators, HD74423 and CO Cam, in important ways. We also study the prior history of this system with binary evolution models and conclude that extensive mass transfer has occurred from the current secondary to the primary.

Pulsation mode switching in the pulsating star HD 81589 and a proposed classification as a field FaRPB star

ABSTRACT Extensive multicolour photometry and low-resolution spectroscopy obtained for HD 81589 place the star in the gap between δ Scuti and slowly pulsating B pulsators on the main sequence. A clear episode of pulsation mode switching has apparently occurred in HD 81589, with its primary pulsation frequency switching from 4.57 to 3.71 c d−1 in less than 6 months. The pulsation frequencies obtained for this star match remarkably well with modelled frequencies of prograde sectoral g-modes for rapidly rotating late B stars on the main sequence. This match, coupled with the rapid rotation rate determined for HD 81589, implies that HD 81589 is one of the first identified fast-rotating pulsating B-type (FaRPB) stars found in the field, complementing the sample of FaRPB stars previously discovered in the open cluster NGC 3766.

Six new rapidly oscillating Ap stars in the Kepler long-cadence data using super-Nyquist asteroseismology

ABSTRACT We perform a search for rapidly oscillating Ap stars in the Kepler long-cadence data, where true oscillations above the Nyquist limit of 283.21 $\mu$Hz can be reliably distinguished from aliases as a consequence of the barycentric time corrections applied to the Kepler data. We find evidence for rapid oscillations in six stars: KIC 6631188, KIC 7018170, KIC 10685175, KIC 11031749, KIC 11296437, and KIC 11409673, and identify each star as chemically peculiar through either pre-existing classifications or spectroscopic measurements. For each star, we identify the principal pulsation mode, and are able to observe several additional pulsation modes in KIC 7018170. We find that KIC 7018170 and KIC 11409673 both oscillate above their theoretical acoustic cut-off frequency, whilst KIC 11031749 oscillates at the cut-off frequency within uncertainty. All but KIC 11031749 exhibit strong amplitude modulation consistent with the oblique pulsator model, confirming their mode geometry and periods of rotation.

HD 96446: a long-period binary with a strongly magnetic He-rich primary with β Cephei pulsations

Aims. HD 96446 is a magnetic B2p He-strong star that has been reported to be a β Cep pulsator. We present a detailed spectroscopic analysis of this object based on an intensive observational data set obtained in a multisite campaign with the spectrographs CORALIE, FEROS, and HARPS (La Silla); UVES (Paranal); HERCULES (Mt. John Observatory); and GIRAFFE (SAAO). Methods. Radial velocities were measured by cross-correlations and analysed to detect periodic variations. On the other hand, the mean spectrum was fit with spectral synthesis to derive atmospheric parameters and chemical abundances. Results. From the analysis of radial velocities, HD 96446 was found to be a spectroscopic binary with a period of 799 days. The stellar companion, which contributes only ∼5% of the total flux, is an A0-type star. A frequency analysis of the radial velocities allowed us to detect two pulsational modes with periods 2.23 h and 2.66 h. The main mode is most probably a low-inclination, dipole mode (l, m) = (1, 0), and the second pulsation mode corresponds to (l, m) = (2, 2) or to a pole-on (l, m) = (3, 2) configuration. In addition to radial velocities, the main pulsation mode is evidenced through small variations in the spectral morphology (temperature variations) and the light flux. The rotation period of 23.4 d, was detected through the variation in line intensities. Chemical abundances are unevenly distributed over the stellar surface, with helium concentrated at the negative magnetic pole and most metals strengthened at lower latitudes. The mean chemical abundance of helium is strongly abnormal, reaching a value of 0.60 (number fraction).

An additional pulsating mode (7.35 mHz) and pulsations timing variations of PG 1613+426

We present the detection of an additional pulsation mode (7.35 mHz) of a subdwarf B star, PG 1613+426, and periodic Observed minus Calculated (O-C) variations for two existing pulsations. PG 1613+426 is near the hot end of the sdB instability strip. One pulsation mode (6.94 mHz) was detected so far by Bonanno et al. (2002) and another pulsation mode candidate (7.05 mHz) was proposed with a confidence level above 90% by Kuassivi and Ferlet (2005). To constrain sdB star evolutional scenarios, this star was monitored in 2010, 2011, 2015, and 2017 as a part of a project for finding companions to sdB stars using the pulsation timing method. The photometric analysis of those data shows an additional 7.35 mHz pulsation mode as well as the previously detected 6.93 mHz mode. However the 7.05 mHz mode was not detected. Nightly amplitude changes of 7.35 mHz mode were observed in the 2011 data, however the 2017 data did not show nightly amplitude shifts. O-C variations were detected in both 6.93 mHz and 7.35 mHz pulsations, indicating that PG 1613+426 may have a low mass companion star. However, more observations are needed to confirm it.