High frequencies in TESS A–F main-sequence stars

Abstract

The driving mechanism for high-frequency oscillations in some chemically peculiar Ap stars, the rapidly oscillating Ap stars (roAp stars), is not understood. The Transiting Exoplanet Survey Satellite mission (TESS) data provide an ideal opportunity to extend the number of roAp stars that might provide further clues to address this problem. From an examination of over 18 000 stars in TESS sectors 1–7, we have discovered high-frequency pulsations in 14 A–F stars, of which only 3 are classified as Ap stars. In addition to these new discoveries, we discuss the frequencies in nine previously known roAp stars. In one of these stars, HD 60435, we confirm a previous finding that the pulsations have lifetimes of only a few days. In another known roAp star, HD 6532, the relative amplitudes of the rotationally modulated sidelobes, which are generally used to estimate the inclination of the magnetic axis relative to the rotational axis, are significantly different from those found in ground-based B-band photometric observations. We also discuss four δ Scuti stars that appear to have independent frequencies similar to those of roAp stars.

TESS cycle 1 observations of roAp stars with 2-min cadence data

“…This final sample was distributed amongst the members of the TESS Asteroseismic Science Consortium (TASC) Working Group 4 (WG4) for detailed analysis to confirm the presence of a positive roAp detection, and to extract rotation periods from the light curves. This process identified 12 new roAp stars previously unreported in the literature and 10 roAp stars discovered through TESS observations and reported by either Cunha et al (2019) or Balona et al (2019). There are also positive detections of pulsations in 31 roAp stars known prior to the launch of TESS, with 3 roAp stars where TESS did not detect pulsational variability as their low amplitude modes are below the TESS detection limit.…”

HD 42659: the only known roAp star in a spectroscopic binary observed with B photometry, TESS, and SALT

“…The TESS photometric observations are the first data which allow us to measure the rotation period of this star. First done by Balona et al (2019), we have refined the fit here to arrive at a rotation period of 2.66265 ± 0.00025 d. This finding allows us to shed some light on the number of nights which Martinez & Kurtz (1994) failed to measure a pulsation; their data, as shown in their table 5 and figure, are separated such that pulsation maximum was often not observed, thus the pulsation was below their detection limit. It was fortunate that they persevered and obtained good rotation phase coverage of the star, although they did not know what that was at the time.…”

Spots and Flares in Hot Main Sequence Stars Observed by Kepler, K2, and TESS

“…The former is a sdB star and the latter is an SX Ari variable (Bp star). Also excluded is the δ Sct flare star TIC 439399707 (Balona et al, 2019b) and the Be X-ray source TIC 207176480 (Balona and Ozuyar, 2020b).…”