Ilkham Galiullin, Antonio C Rodriguez, Shrinivas R Kulkarni, Rashid Sunyaev, Marat Gilfanov, Ilfan Bikmaev, Lev Yungelson, Jan van Roestel, Boris T Gänsicke, Irek Khamitov, Paula Szkody, Kareem El-Badry, Mikhail Suslikov, Thomas A Prince, Mikhail Buntov, Ilaria Caiazzo, Mark Gorbachev, Matthew J Graham, Rustam Gumerov, Eldar Irtuganov, Russ R Laher, Pavel Medvedev, Reed Riddle, Ben Rusholme, Nail Sakhibullin, Alexander Sklyanov, Zachary P Vanderbosch

A Joint SRG/eROSITA + ZTF search: Discovery of a 97-min period eclipsing cataclysmic variable with evidence of a brown dwarf secondary

  • Space and Planetary Science
  • Astronomy and Astrophysics

Abstract Cataclysmic variables (CVs) that have evolved past the period minimum during their lifetimes are predicted to be systems with a brown dwarf donor. While population synthesis models predict that around ≈40–70% of the Galactic CVs are post-period minimum systems referred to as ”period bouncers”, only a few dozen confirmed systems are known. We report the study and characterisation of a new eclipsing CV, SRGeJ041130.3+685350 (SRGeJ0411), discovered from a joint SRG/eROSITA and ZTF program. The optical spectrum of SRGeJ0411 shows prominent hydrogen and helium emission lines, typical for CVs. We obtained optical high-speed photometry to confirm the eclipse of SRGeJ0411 and determine the orbital period to be Porb ≈ 97.530 minutes. The spectral energy distribution suggests that the donor has an effective temperature of ≲ 1, 800 K. We constrain the donor mass with the period–density relationship for Roche-lobe-filling stars and find that Mdonor ≲ 0.04 M⊙. The binary parameters are consistent with evolutionary models for post-period minimum CVs, suggesting that SRGeJ0411 is a new period bouncer. The optical emission lines of SRGeJ0411 are single-peaked despite the system being eclipsing, which is typically only seen due to stream-fed accretion in polars. X-ray spectroscopy hints that the white dwarf in SRGeJ0411 could be magnetic, but verifying the magnetic nature of SRGeJ0411 requires further investigation. The lack of optical outbursts has made SRGeJ0411 elusive in previous surveys, and joint X-ray and optical surveys highlight the potential for discovering similar systems in the near future.

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