A brown dwarf donor and an optically thin accretion disc with a complex stream impact region in the period-bouncer candidate BW Sculptoris

Abstract

We present an analysis of multi-epoch spectroscopic and photometric observations of the WZ Sge-type dwarf nova BW Scl, a period-bouncer candidate. We detected multiple irradiation-induced emission lines from the donor star allowing the radial velocity variations to be measured with high accuracy. Also, using the absorption lines Mgii 4481 and Caii K originated in the photosphere of the accreting white dwarf (WD), we measured the radial velocity semi-amplitude of the WD and its gravitational redshift. We find that the WD has a mass of 0.85$\pm$0.04 M${}_{\odot }$, while the donor is a low-mass object with a mass of 0.051$\pm$0.006 M${}_{\odot }$, well below the hydrogen-burning limit. Using NIR data, we put an upper limit on the effective temperature of the donor to be $\lesssim$1600 K, corresponding to a brown dwarf of T spectral type. The optically thin accretion disc in BW Scl has a very low luminosity $\lesssim$4 $\times 10^{30}$ erg s${}^{-1}$ which corresponds to a very low mass accretion rate of $\lesssim$7 $\times 10^{-13}$ M${}_{\odot }$ year${}^{-1}$. The outer parts of the disc have a low density allowing the stream to flow down to the inner disc regions. The brightest part of the hotspot is located close to the circularization radius of the disc. The hotspot is optically thick and has a complex, elongated structure. Based on the measured system parameters, we discuss the evolutionary status of the system.

Minor changes to match the version published in MNRAS. Supplementary figures (dynamical Doppler maps) available at https://vitaly.neustroev.net/researchfiles/bwscl/

References in corpus (22)

• Estimating distances from parallaxes. V: Geometric and photogeometric distances to 1.47 billion stars in Gaia Early Data Release 3
• Initial Performance of the NEOWISE Reactivation Mission
• Molecfit: A general tool for telluric absorption correction. I. Method and application to ESO instruments
• Molecfit: A general tool for telluric absorption correction II. Quantitative evaluation on ESO-VLT X-Shooter spectra
• PESSTO : survey description and products from the first data release by the Public ESO Spectroscopic Survey of Transient Objects
• White Dwarf Mass Distribution in the SDSS
• On the Spectral Evolution of Hot White Dwarf Stars. I. A Detailed Model-Atmosphere Analysis of Hot White Dwarfs from SDSS DR12
• Atomic Diffusion and Mixing in Old Stars I. VLT/FLAMES-UVES Observations of Stars in NGC 6397
• Population Synthesis of Cataclysmic Variables: I. Inclusion of Detailed Nuclear Evolution
• Effective Temperatures of Cataclysmic Variable White Dwarfs as a Probe of their Evolution
• The evolutionary status of Cataclysmic Variables: Eclipse modelling of 15 systems
• Evidence for reduced magnetic braking in polars from binary population models
• gPhoton: The GALEX Photon Data Archive
• Gravity and limb-darkening coefficients for compact stars: DA, DB, and DBA eclipsing white dwarfs
• The white dwarf mass-radius relation and its dependence on the hydrogen envelope
• Evolutionary models for ultracool dwarfs
• Cyclic brightening in the short-period WZ Sge-type cataclysmic variable SDSS J080434.20+510349.2
• Evidence for mass accretion driven by spiral shocks onto the white dwarf in SDSS J123813.73-033933.0
• The remarkable outburst of the highly evolved post-period-minimum dwarf nova SSS J122221.7-311525
• BF Eridani: a cataclysmic variable with a massive white dwarf and an evolved secondary
• Planetary Nebula Candidates in Extragalactic Young Star Clusters
• Evolution of short-period cataclysmic variables: implications from eclipse modeling and stage A superhump method (with New Year's gift)

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• Cataclysmic variables around the period-bounce: An eROSITA-enhanced multi-wavelength catalog
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• Gaia white dwarfs with infrared excess I. The 100 pc catalogue
• eROSITA-selection of new period-bounce Cataclysmic Variables: First follow-up confirmation using TESS and SDSS
• A Mass Transferring Brown Dwarf Binary on a 57 Minute Orbit
• Fates of the sub-stellar objects (FOSSO) I. Fates of the known brown dwarfs in main-sequence--BD binaries
• Detectability of continuous gravitational waves from planetary-mass companions orbiting compact stars