Short-period pulsating hot-subdwarf stars observed by TESS I. Southern ecliptic hemisphere

TL;DR

This study uses TESS data to identify and analyze 43 short-period pulsating hot subdwarf stars in the southern ecliptic hemisphere, including the first He-sdOB star with such pulsations, advancing understanding of their internal structure and evolution.

Contribution

It reports the first detection of short-period pulsations in a He-sdOB star and provides a comprehensive catalog of pulsators, including hybrid types, from TESS observations.

Findings

Identified 43 short-period hot subdwarf pulsators.

First He-sdOB star with short-period pulsations.

Detected potential stellar rotation periods in four candidates.

Abstract

We present results of a Transiting Exoplanet Survey Satellite (TESS) search for short-period pulsations in compact stellar objects observed in years 1 and 3 of the TESS mission, during which the southern ecliptic hemisphere was targeted. We describe the TESS data used and the details of the search method. For many of the targets, we use unpublished spectroscopic observations to classify the objects. From the TESS photometry, we clearly identify 43 short-period hot-subdwarf pulsators, including 32 sdB stars, eight sdOB stars, two sdO stars, and, significantly, one He-sdOB star, which is the first of this kind to show short-period pulsations. Eight stars show signals at both low and high frequencies, and are therefore ``hybrid'' pulsators. We report the list of prewhitened frequencies and we show the amplitude spectra calculated from the TESS data. We make an attempt to identify possible multiplets caused by stellar rotation, and we select four candidates with rotation periods between 1 and 12.9d. The most interesting targets discovered in this survey should be observed throughout the remainder of the TESS mission and from the ground. Asteroseismic investigations of these data sets will be invaluable in revealing the interior structure of these stars and will boost our understanding of their evolutionary history. We find three additional new variable stars but their spectral and variability types remain to be constrained.