Unveiling the period-bounce population of cataclysmic variables: Spectroscopic and time-domain follow-up of eROSITA-selected candidates
Abstract
During their secular evolution, cataclysmic variable stars (CVs) evolve toward shorter orbital periods (Porb) until reaching a minimum near Porb∼80 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 Porb 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 ∼ 50%. Our results suggest that a substantial fraction of the PB population may remain hidden in WD catalogues.
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BibTeX
@misc{hernandezdiaz2026unveiling,
title = {{Unveiling the period-bounce population of cataclysmic variables: Spectroscopic and time-domain follow-up of eROSITA-selected candidates}},
author = {S. Hernández-Díaz and B. Stelzer and A. Schwope and D. Muñoz-Giraldo and M. R. Schreiber and J. Brink and K. G. Pradeep and B. T. Gänsicke and M. Eracleous and K. Szekerczes and S. F. Anderson and J. R. Brownstein},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2607.27855},
eprint = {2607.27855},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2607.27855},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Unveiling the period-bounce population of cataclysmic variables: Spectroscopic and time-domain follow-up of eROSITA-selected candidates
AU - S. Hernández-Díaz
AU - B. Stelzer
AU - A. Schwope
AU - D. Muñoz-Giraldo
AU - M. R. Schreiber
AU - J. Brink
AU - K. G. Pradeep
AU - B. T. Gänsicke
AU - M. Eracleous
AU - K. Szekerczes
AU - S. F. Anderson
AU - J. R. Brownstein
PY - 2026
DA - 2026/09/15
PB - arXiv
DO - 10.48550/arxiv.2607.27855
UR - https://arxiv.org/abs/2607.27855
AB - During their secular evolution, cataclysmic variable stars (CVs) evolve toward shorter orbital periods (P_orb) until reaching a minimum near P_orb∼80 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 ∼ 50%. Our results suggest that a substantial fraction of the PB population may remain hidden in WD catalogues.
ER -