A Joint SRG/eROSITA + ZTF Search: Discovery of a 97-min Period Eclipsing Cataclysmic Variable with Evidence of a Brown Dwarf Secondary

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 $\approx 40-70\%$ 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 $P_{\text{orb}}\approx 97.530$ minutes. The spectral energy distribution suggests that the donor has an effective temperature of $\lesssim 1,800$ K. We constrain the donor mass with the period--density relationship for Roche-lobe-filling stars and find that $M_{\text{donor}}\lesssim 0.04M_{\odot }$. 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.

17 pages, 16 figures, accepted to MNRAS

References in corpus (31)

• Array Programming with NumPy
• Gaia Data Release 3: Summary of the content and survey properties
• Estimating distances from parallaxes. V: Geometric and photogeometric distances to 1.47 billion stars in Gaia Early Data Release 3
• The eROSITA X-ray telescope on SRG
• astroquery: An Astronomical Web-Querying Package in Python
• Second ROSAT all-sky survey (2RXS) source catalogue
• The SRG X-ray orbital observatory, its telescopes and first scientific results
• The unWISE Catalog: Two Billion Infrared Sources from Five Years of WISE Imaging
• Magnetic White Dwarfs
• White Dwarf Mass Distribution in the SDSS
• Population Synthesis of Cataclysmic Variables: I. Inclusion of Detailed Nuclear Evolution
• Measurements of Physical Parameters of White Dwarfs: A Test of the Mass-Radius Relation
• A brown dwarf mass donor in an accreting binary
• Model Atmospheres From Very Low Mass Stars to Brown Dwarfs
• Evidence for reduced magnetic braking in polars from binary population models
• Constraints on the space density of intermediate polars from the Swift-BAT survey
• Photometric brown-dwarf classification. I. A method to identify and accurately classify large samples of brown dwarfs without spectroscopy
• The nature of the close magnetic white dwarf + probable brown dwarf binary SDSS J121209.31+013627.7
• Birth of the ELMs: a ZTF survey for evolved cataclysmic variables turning into extremely low-mass white dwarfs
• A Near-Infrared Spectroscopic Study of the Accreting Magnetic White Dwarf SDSS J121209.31+013627.7 and its Substellar Companion
• Period bouncers as detached magnetic cataclysmic variables
• X-ray orbital modulation of a white dwarf accreting from an L dwarf: The system SDSS J121209.31+013627.7
• Exploratory Spectroscopy of Magnetic Cataclysmic Variables Candidates and Other Variable Objects
• Discovery of Two Polars from a Crossmatch of ZTF and the SRG/eFEDS X-ray Catalog
• A brown dwarf donor and an optically thin accretion disc with a complex stream impact region in the period-bouncer candidate BW Sculptoris
• New X-ray detections of magnetic period-bounce cataclysmic variables from XMM-Newton and SRG/eROSITA
• Discovery of eRASSt J192932.9-560346: a bright, two-pole accreting, eclipsing polar
• Identification of 3 cataclysmic variables detected by the ART-XC and eROSITA telescopes aboard SRG during the all-sky X-ray survey
• X-ray observations of historical classical nova counterparts with eROSITA telescope aboard SRG orbital observatory during the all-sky survey
• X-ray and ultraviolet observations of the eclipsing cataclysmic variables OV Bootis and SDSS J103533.02+055158.3 with degenerate donors
• SRGe2149+6736 -- the new candidate to AM~Her type variables discovered by eROSITA telescope on "Spectrum--Roentgen--Gamma" orbital observatory

Cited by in corpus (7)

• Discovery and characterization of ZTF J0112+5827: An 80.9-minute polar with strong cyclotron features
• Magnetic braking below the cataclysmic variable period gap and the observed dearth of period bouncers
• Cataclysmic Variable Candidates Identified in eROSITA-DE DR1,XMM-Newton, Swift, and ROSAT Catalogs
• A Mass Transferring Brown Dwarf Binary on a 57 Minute Orbit
• eROSITA-selection of new period-bounce Cataclysmic Variables: First follow-up confirmation using TESS and SDSS
• Multiwavelength Characterization of a New Magnetic Cataclysmic Variable 2CXO J050740.7-091337
• Detectability of continuous gravitational waves from planetary-mass companions orbiting compact stars