University of Oulu

Vitaly V Neustroev , Iikka Mäntynen, A brown dwarf donor and an optically thin accretion disc with a complex stream impact region in the period-bouncer candidate BW Sculptoris, Monthly Notices of the Royal Astronomical Society, Volume 523, Issue 4, August 2023, Pages 6114–6137,

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

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Author: Neustroev, Vitaly V1; Mäntynen, Iikka1,2
Organizations: 1Space Physics and Astronomy research unit, PO Box 3000, FI-90014 University of Oulu, Finland
2Department of Physics and Astronomy, University of Turku, FI-20014 Turku, Finland
Format: article
Version: published version
Access: open
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Language: English
Published: Oxford University Press, 2023
Publish Date: 2023-08-21


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 Mg II 4481 Å and Ca II 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 ± 0.04 M⊙, while the donor is a low-mass object with a mass of 0.051 ± 0.006 M⊙, well below the hydrogen-burning limit. Using NIR data, we put an upper limit on the effective temperature of the donor to be ≲1600 K, corresponding to a brown dwarf of T spectral type. The optically thin accretion disc in BW Scl has a very low luminosity ≲4 × 10³⁰ erg s⁻¹ which corresponds to a very low-mass accretion rate of ≲7 × 10⁻¹³ M⊙ yr⁻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.

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Series: Monthly notices of the Royal Astronomical Society
ISSN: 0035-8711
ISSN-E: 1365-8711
ISSN-L: 0035-8711
Volume: 523
Issue: 4
Pages: 6114 - 6137
DOI: 10.1093/mnras/stad1730
Type of Publication: A1 Journal article – refereed
Field of Science: 115 Astronomy and space science
Funding: We would like to thank the anonymous referee for useful comments. VN acknowledges the financial support from the visitor and mobility program of the Finnish Centre for Astronomy with ESO (FINCA), funded by the Academy of Finland grant nr 306531. Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under programme IDs 068.D-0153, 069.D-0391, 086.D-0775, 100.D-0932, and 101.D-0806. This paper includes data collected by the TESS mission, which are publicly available from the Mikulski Archive for Space Telescopes (MAST). Funding for the TESS mission is provided by the NASA's Science Mission Directorate. This publication makes use of data products from the Wide-field Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administration. This publication also makes use of data products from NEOWISE, which is a project of the Jet Propulsion Laboratory/California Institute of Technology, funded by the Planetary Science Division of the National Aeronautics and Space Administration. This research made use of StarCAT, hosted by the MAST. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. We thank the Swift PI, Brad Cenko, for approving the observations, and the Swift planning and operations teams for their ongoing support. We acknowledge with thanks the variable star observations from the AAVSO International Data base contributed by observers worldwide and used in this research.
Copyright information: © 2023 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.