Abstract

Contributed Talk - Splinter StellarEndpoints   (MW-2235)

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

S. Hernández-Díaz (1), B. Stelzer (1), A. Schwope (2), D. Muñoz-Giraldo (1), M. R. Schreiber (3), J. Brink (2, 4), K. G. Pradeep (2, 4), B. T. Gänsicke (5), M. Eracleous (6), K. Szekerczes (6), S. F. Anderson (7), and J. R. Brownstein (8)
(1) Institut für Astronomie und Astrophysik, Eberhard Karls Universität Tübingen, Sand 1, 72076 Tübingen, Germany; (2) Leibniz Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany; (3) Universidad Técnica Federico Santa María (UTFSM), Department of Physics, Av. España 1680, Valparaíso, Chile; (4) Institute for Physics and Astronomy, University of Potsdam, Karl- Liebknecht-Str. 24/25, 14476 Potsdam, Germany; (5) Department of Physics, University of Warwick, Coventry, CV4 7AL, UK; (6) 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; (7) Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195, USA; (8) Department of Physics and Astronomy, University of Utah, 115 S. 1400 E., Salt Lake City, UT 84112, USA

Cataclysmic variables (CVs) are compact binaries in which a white dwarf (WD) accretes from a Roche-lobe-filling low-mass donor. They evolve toward shorter orbital periods ($P_{ m orb}$) until reaching a minimum near $sim$80 min, after which they “bounce back” to longer periods as the donor becomes out of thermal equilibrium or increasingly degenerate. These evolved systems, known as period-bouncers (PBs), are predicted to comprise 40–80\% of the CV population, yet only 3–25\% have been observationally confirmed. To uncover this missing population, we selected 213 high-likelihood PB candidates by cross-matching the eROSITA X-ray and extit{Gaia} WD catalogues and classifying them on a multiwavelength scorecard. We present the results from an ongoing optical spectroscopic follow-up campaign of these objects with SDSS-V, complemented by archival time-series photometry from TESS, ZTF, CRTS, ASAS-SN, and ATLAS, together with multiwavelength photometry for SED analysis. We report the confirmation of 24 new CVs via Balmer line emission or outburst activity, and identify two systems as strong PB candidates based on $P_{ m orb}$ measurements and photometric constraints on the donor SpT. We also identify three systems that may represent PBs approaching detachment after the onset of WD magnetism. Finally, we present a new diagnostic based on Balmer decrements to distinguish PBs from pre-bounce CVs. We find that 17 new CVs observed with SDSS-V are consistent with being PBs, potentially increasing the PB population by $sim$50\% and indicating that a substantial fraction of the PB population remains hidden in WD catalogues.