A comprehensive search for hot subdwarf stars using Gaia and TESS

II. Uncovering new pulsators and close binary systems

¹ Astronomical Observatory, Jagiellonian University, ul. Orla 171, 30-244 Krakow, Poland
² Institute of Astronomy, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
³ Astroserver.org, Fő tér 1, 8533 Malomsok, Hungary
⁴ Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
⁵ INAF-Osservatorio Astrofisico di Torino, strada dell’Osservatorio 20, 10025 Pino Torinese, Italy
⁶ Instituto de Física y Astronomía, Universidad de Valparaíso, Gran Bretaña 1111, Playa Ancha, Valparaíso 2360102, Chile
⁷ Institute for Physics and Astronomy, University of Potsdam, Karl-Liebknecht-Str. 24/25, 14476 Potsdam, Germany
⁸ Jagiellonian University, Doctoral School of Exact and Natural Sciences, ul. S. Lojasiewicza 11, 30-348 Krakow, Poland
⁹ Mt. Suhora Astronomical Observatory, University of the National Education Commission, ul. Podchorążych 2, 30-084 Kraków, Poland
¹⁰ Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Konkoly-Thege Miklós ut 15–17, 1121 Budapest, Hungary

^★ Corresponding authors: jk@oa.uj.edu.pl; muratuzundag.astro@gmail.com

Received: 14 October 2024
Accepted: 16 June 2025

Abstract

Context. Hot subdwarfs are compact, evolved stars that serve as critical testbeds for understanding binary evolution, stellar remnants, and pulsation physics. Their formation is often attributed to binary interactions, but a significant fraction are apparently single, suggesting multiple formation pathways. Pulsating hot subdwarfs, whether in binaries or single, offer valuable opportunities for asteroseismic investigations to probe their internal structure and evolution.

Aims. We aim to expand the known population of pulsating hot subdwarfs and explore their formation channels by investigating both binary and single systems.

Methods. Using TESS light curves, we conducted a systematic variability search for hot subdwarf candidates identified from Gaia EDR3 and the TESS Input Catalogue. Variability was assessed using periodograms and applying a S/N > 5 threshold. Stars with multiple frequencies were classified as pulsators, while single-frequency sources were checked for binarity signatures such as harmonics or eclipses. Variability detections were verified with the TESS-Localize tool. Additionally, we performed follow-up spectroscopy for 11 targets, and carried out spectral energy distribution (SED) fitting to constrain the binary nature and fundamental stellar parameters.

Results. We present 42 new variable hot subdwarfs, including 22 pulsators, 3 candidates for pulsating hot subdwarfs in binary systems (including one sdO star), and 13 additional binary candidates. The variability of 4 stars remains to be confirmed. Our spectroscopic and SED analyses of 11 stars provide improved constraints on stellar parameters and reveal new details about their binary nature.

Conclusions. This work significantly expands the sample of known pulsating hot subdwarfs and binary candidates and demonstrates the importance of combined space-based photometry and ground-based follow-up in understanding the formation and evolution of hot subdwarf stars.