Rotation and pulsation in Ap stars: first light results from TESS sectors 1 and 2

Abstract

We present the first results from the Transiting Exoplanet Survey Satellite (TESS) on the rotational and pulsational variability of magnetic chemically peculiar A-type stars. We analyse TESS 2-min cadence data from sectors 1 and 2 on a sample of 83 stars. Five new rapidly oscillating Ap (roAp) stars are announced. One of these pulsates with periods around 4.7 min, making it the shortest period roAp star known to date. Four out of the five new roAp stars are multiperiodic. Three of these, and the singly-periodic one show the presence of rotational mode splitting. Individual frequencies are provided in all cases. In addition, seven previously known roAp stars are analysed. Additional modes of oscillation are found in some stars, while in others we are able to distinguish the true pulsations from possible aliases present in the ground-based data. We find that the pulsation amplitude in the TESS filter is typically a factor 6 smaller than that in the B filter which is usually used for ground-based observations. For four roAp stars we set constraints on the inclination angle and magnetic obliquity, through the application of the oblique pulsator model. We also confirm the absence of roAp-type pulsations down to amplitude limits of 6 and 13 µmag, respectively, in two of the best characterised non-oscillating Ap (noAp) stars. We announce 27 new rotational variables along with their rotation periods, and provide different rotation periods for seven other stars. Finally, we discuss how these results challenge state-of-the-art pulsation models for roAp stars.

The first view of δ Scuti and γ Doradus stars with the TESS mission

“…More recently, the successful launch of TESS and the delivery of the first TESS mission data (Ricker et al 2014(Ricker et al , 2015, which are in the southern ecliptic hemisphere, provide new insight into pulsation and rotation in intermediate-mass stars (e.g. Cunha et al 2019;Sikora et al 2019). The primary mission of TESS follows the groundwork of the Kepler mission, and aims to detect planetary transits in the brightest stars across the sky.…”

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.…”

“…The distinction between roAp stars and chemically peculiar δ Scuti stars based on photometric data alone is becoming less clear (e.g. Balona et al 2019). Typically, an Ap star showing rapid pulsations was historically sufficient to classify a roAp star.…”

“…As such, this mission represents a tremendous opportunity to not only significantly increase the sample size of known pulsating Ap stars (see e.g. Cunha et al 2019), but also, given the exquisite data quality, to perform a detailed characterization of specific objects of interest.…”

“…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.…”