TESS Cycle 2 observations of roAp stars with 2-min cadence data

TL;DR

This study systematically analyzes TESS Cycle 2 data to discover new rapidly oscillating Ap stars, revealing their pulsation characteristics, variability, and incidence rate, thus advancing understanding of stellar pulsations in chemically peculiar stars.

Contribution

It reports seven new roAp stars, analyzes known and new pulsators, and provides the most comprehensive TESS-based survey of roAp stars to date.

Findings

Identified 7 new roAp stars in TESS data.

Almost 70% of the studied roAp stars are α^2 CVn-type variables.

The incidence rate of roAp stars among Ap stars is approximately 5.5%.

Abstract

We present the results of a systematic search of the Transiting Exoplanet Survey Satellite (TESS) 2-min cadence data for new rapidly oscillating Ap (roAp) stars observed during the Cycle 2 phase of its mission. We find seven new roAp stars previously unreported as such and present the analysis of a further 25 roAp stars that are already known. Three of the new stars show multiperiodic pulsations, while all new members are rotationally variable stars, leading to almost 70 per cent (22) of the roAp stars presented being $\alpha^2$ CVn-type variable stars. We show that targeted observations of known chemically peculiar stars are likely to overlook many new roAp stars, and demonstrate that multi-epoch observations are necessary to see pulsational behaviour changes. We find a lack of roAp stars close to the blue edge of the theoretical roAp instability strip, and reaffirm that mode instability is observed more frequently with precise, space-based observations. In addition to the Cycle 2 observations, we analyse TESS data for all known roAp stars. This amounts to 18 further roAp stars observed by TESS. Finally, we list six known roAp stars that TESS is yet to observe. We deduce that the incidence of roAp stars amongst the Ap star population is just 5.5 per cent, raising fundamental questions about the conditions required to excite pulsations in Ap stars. This work, coupled with our previous work on roAp stars in Cycle 1 observations, presents the most comprehensive, homogeneous study of the roAp stars in the TESS nominal mission, with a collection of 112 confirmed roAp stars in total.