Daniela Muñoz Giraldo, Space-based Astrophysics (SBA) Group, IAAT — July 1, 2024

Period-bounce cataclysmic variables (CVs) are systems where a white dwarf accretes from a brown dwarf donor, having reached a point where the degeneracy of the donor reverses the orbit period evolution. A large portion of the CV population, between 40% and 70%, is predicted to be made up of period-bouncers. However, due to their intrinsic faintness, only on the order of a dozen such systems have been confidently identified so far. A promising approach to identify period-bounce CVs is an X-ray detection. It provides proof of accretion from the substellar companion onto the white dwarf because the coronal emission of a brown dwarf donor is below the sensitivity of current instruments.

A three step approach is taken in order to bring the number of observed and expected period-bouncers into agreement. First, we performed a detailed study of a pilot-sample of magnetic period-bouncers using X-rays in order to establish specific X-ray characteristics of this elusive class of CVs. Second, we compiled a literature catalog of CVs around the period-bounce, including known period-bouncers, in order to produce a "scorecard" assigning to each system the probability of being a period-bouncer. We systematically analysed X-ray data from the recent all-sky surveys carried out with the extended ROentgen Survey with an Imaging Telescope Array (eROSITA) onboard the Spektrum-Roentgen-Gamma spacecraft (SRG) to confirm new period-bouncers. And third, we began compiling a catalog of new period-bounce candidates detected by eROSITA that after confirmation from follow-up surveys should lead to the identification of the missing population of period-bouncers.