A search for variable subdwarf B stars in TESS Full Frame Images -- I. Variable objects in the southern ecliptic hemisphere

TL;DR

This study used TESS Full Frame Images to search for variable subdwarf B stars in the southern ecliptic hemisphere, discovering new pulsators, binaries, and variable objects, with only two confirmed sdB pulsators.

Contribution

First large-scale search for pulsating subdwarf B stars in TESS FFI data, identifying new variable objects and candidates for further study.

Findings

Discovered 2 new sdB pulsators and 26 known sdB variables.

Identified 83 non-classified pulsating stars and 83 eclipsing binaries.

Found 1807 variable objects, including novae and other spectral types.

Abstract

We report the results of our search for pulsating subdwarf B stars in Full Frame Images, sampled at 30 min cadence and collected during Year 1 of the TESS mission. Year 1 covers most of the southern ecliptic hemisphere. The sample of objects we checked for pulsations was selected from a subdwarf B stars database available to public. Only two positive detections have been achieved, however, as a by-product of our search we found 1807 variable objects, most of them not classified, hence their specific variability class cannot be confirmed at this stage. Our preliminary discoveries include: two new subdwarf B (sdB) pulsators, 26 variables with known sdB spectra, 83 non-classified pulsating stars, 83 eclipsing binaries (detached and semi-detached), a mix of 1535 pulsators and non-eclipsing binaries, two novae, and 77 variables with known (non-sdB) spectral classification. Among eclipsing binaries we identified two known HW Vir systems and four new candidates. The amplitude spectra of the two sdB pulsators are not rich in modes, but we derive estimates of the modal degree for one of them. In addition, we selected five sdBV candidates for mode identification among 83 pulsators and describe our results based on this preliminary analysis. Further progress will require spectral classification of the newly discovered variable stars, which hopefully include more subdwarf B stars.