A Joint SRG/eROSITA + ZTF Search: Discovery of a 97-min Period Eclipsing Cataclysmic Variable with Evidence of a Brown Dwarf Secondary
arxiv(2024)
摘要
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 P_orb≈ 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
M_donor≲ 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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