Journal
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Volume 470, Issue 1, Pages 732-741Publisher
OXFORD UNIV PRESS
DOI: 10.1093/mnras/stx741
Keywords
stars: carbon; stars: evolution; stars: individual: OW J175358.85-310728.9; stars: magnetic field; stars: rotation; white dwarfs
Categories
Funding
- Erasmus Mundus Programme SAPIENT
- National Research Foundation of South Africa (NRF)
- Nederlandse Organisatie voor Wetenschappelijk Onderzoek (the Dutch Organisation for Science Research), Radboud University
- University of Cape Town
- NSERC (Canada)
- Northern Ireland Executive
- ESO Telescopes at the La Silla Paranal Observatory [093.D-0753(A), 177.D-3023]
- Southern African Large Telescope (SALT) [2016-1-SCI-015]
- NWO/NRF
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We present the discovery and follow-up observations of the second known variable warm DQ white dwarf OWJ175358.85-310728.9 (OWJ1753-3107). OWJ1753-3107 is the brightest of any of the currently known warm or hot DQ and was discovered in the Omega White Survey as exhibiting optical variations on a period of 35.5452 (2) min, with no evidence for other periods in its light curves. This period has remained constant over the last 2 yr and a single-period sinusoidal model provides a good fit for all follow-up light curves. The spectrum consists of a very blue continuum with strong absorption lines of neutral and ionized carbon, a broad He I lambda 4471 line and possibly weaker hydrogen lines. The CI lines are Zeeman split, and indicate the presence of a strong magnetic field. Using spectral Paschen-Back model descriptions, we determine that OWJ1753-3107 exhibits the following physical parameters: T-eff = 15 430 K, log (g) = 9.0, log (N(C)/N(He))=-1.2 and the mean magnetic field strength is B-z = 2.1 MG. This relatively low temperature and carbon abundance (compared to the expected properties of hot DQs) is similar to that seen in the other warm DQ SDSS J1036+6522. Although OW J1753-3107 appears to be a twin of SDSS J1036+ 6522, it exhibits a modulation on a period slightly longer than the dominant period in SDSS J1036+ 6522 and has a higher carbon abundance. The source of variations is uncertain, but they are believed to originate from the rotation of the magnetic white dwarf.
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