MOBSTER – II. Identification of rotationally variable A stars observed with TESS in sectors 1–4

Abstract

Recently, high-precision optical 2 min cadence light curves obtained with TESS for targets located in the mission's defined first four sectors have been released. The majority of these high-cadence and high-precision measurements currently span ∼ 28 d, thereby allowing periodic variability occurring on timescales 14 d to potentially be detected. Magnetic chemically peculiar (mCP) A-type stars are well known to exhibit rotationally modulated photometric variability that is produced by inhomogeneous chemical abundance distributions in their atmospheres. While mCP stars typically exhibit rotation periods that are significantly longer than those of non-mCP stars, both populations exhibit typical periods 10 d; therefore, the early TESS releases are suitable for searching for rotational modulation of the light curves of both mCP and non-mCP stars. We present the results of our search for A-type stars that exhibit variability in their TESS light curves that is consistent with rotational modulation based on the first two data releases obtained from sectors 1 to 4. Our search yielded 134 high-probability candidate rotational variables -60 of which have not been previously reported. Approximately half of these stars are identified in the literature as Ap (mCP) stars. Comparisons between the subsample of high-probability candidate rotationally variable Ap stars and the subsample of stars that are not identified as Ap reveal that the latter subsample exhibits statistically (i) shorter rotation periods and (ii) significantly lower photometric amplitudes.

Horizontal spreading of planetary debris accreted by white dwarfs

“…All in all, there is no robust evidence of surface metal heterogeneities at white dwarfs. This is in contrast with magnetic chemically peculiar main sequence stars where inhomogeneities are routinely detected (see, e.g., Sikora et al 2019).…”

A plethora of new, magnetic chemically peculiar stars from LAMOST DR4

“…Since then, several studies have identified new mCP stars on a minor scale (e.g. Hümmerich et al 2018;Scholz et al 2019;Sikora et al 2019) but no large scale spectroscopic surveys have been conducted during the past recent decades that aim specifically at the identification of new mCP stars "en masse".…”

Rotational and pulsational variability in the TESS light curve of HD 27463

“…This is because the heat-engine driving mechanism operating in the He II ionization zone is closer to the surface and is more efficient at exciting higher radial orders, hence higher frequencies, in hotter δ Scuti stars (Pamyatnykh 2000;Dupret et al 2019). Cunha et al (2019) and Sikora et al (2019) have also classified this star as a suspected δ Scuti variable. Therefore, our spectroscopic parameters and subsequent modelling results are in agreement with this theoretically predicted and observed relationship.…”

“…Previous surveys designed to detect high-frequency pulsations did not yield any detection in this star (Martinez & Kurtz 1994;Joshi et al 2016). However, using TESS data, Cunha et al (2019) and Sikora et al (2019) have classified HD 27463 as a suspected new δ Scuti variable. Therefore, in this study, we set out to perform a more involved investigation of this star's TESS photometry, in conjunction with high-resolution spectroscopy.…”