Unveiling the period-bounce population of cataclysmic variables: Spectroscopic and time-domain follow-up of eROSITA-selected candidates

arXiv:2607.27855 · astro-ph.SR · Submitted 2026-07-30 · Read on arXiv

Institut für Astronomie und Astrophysik, Eberhard Karls Universität Tübingen, Sand 1, 72076 Tübingen, Germany · Institut für Astronomie und Astrophysik, Eberhard Karls Universität Tübingen, Sand 1, 72076 Tübingen, Germany · Leibniz Institut für Astrophysik Potsdam · Institut für Astronomie und Astrophysik, Eberhard Karls Universität Tübingen, Sand 1, 72076 Tübingen, Germany · Universidad Técnica Federico Santa María · Institute for Physics and Astronomy, University of Potsdam, Karl-Liebknecht-Str. 24/25, 14476 Potsdam, Germany · Institute for Physics and Astronomy, University of Potsdam, Karl-Liebknecht-Str. 24/25, 14476 Potsdam, Germany · Department of Physics, University of Warwick, Coventry, CV4 7AL, UK · Department of Astronomy and Astrophysics and Institute for Gravitation and the Cosmos, Penn State University, 525 Davey Lab, 251 Pollock Road, University Park, PA 16802, USA · Department of Astronomy and Astrophysics and Institute for Gravitation and the Cosmos, Penn State University, 525 Davey Lab, 251 Pollock Road, University Park, PA 16802, USA · Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195, USA · Department of Physics and Astronomy, University of Utah, 115 S.1400 E., Salt Lake City, UT 84112, USA

astro-ph.SR

Submitted: 2026-07-30

Updated: 2026-09-15

Comments: 20 pages, 9 figures. Accepted for publication in A&A

License: http://creativecommons.org/licenses/by/4.0/

The gist: During their secular evolution, cataclysmic variable stars (CVs) evolve toward shorter orbital periods (P orb) until reaching a minimum near P orb about80 min, after which they evolve back toward

Terminology

Abstract

During their secular evolution, cataclysmic variable stars (CVs) evolve toward shorter orbital periods (P orb) until reaching a minimum near P orb about80 min, after which they evolve back toward longer periods. CVs that have evolved past this evolutionary turning point are known as period-bouncers (PBs). Despite predictions that 40-80% of all CVs should be PBs, only 3-25% of the observed CV population is composed of PBs, a discrepancy likely due to their intrinsic low luminosities. We aim to investigate the evolutionary status of 213 SRG/eROSITA-selected PB candidates. The sample also includes 19 previously confirmed PBs, which serve as benchmarks for evaluating the candidates. We confirmed 24 new CVs through the identification of Balmer emission lines in optical spectra from the Sloan Digital Sky Survey V (SDSS-V) and of dwarf-nova outbursts in archival photometric surveys. By fitting hydrogen-rich atmosphere models to the SDSS-V spectra, we estimated the effective temperature and secular mass accretion rate of the WDs. We also measured the Balmer decrements, used as diagnostics of the physical conditions of the accretion disc, to assess whether they are consistent with known PBs. In addition, we analysed archival light curves from the Transiting Exoplanet Survey Satellite (TESS) to determine P orb for a subset of systems, and compiled multi-wavelength photometry to construct and model spectral energy distributions (SEDs), from which we inferred approximate donor spectral types. Our analysis of the new CVs indicates that they are consistent with being PBs, potentially increasing the population of confirmed PBs by about 50%. Our results suggest that a substantial fraction of the PB population may remain hidden in WD catalogues.

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