New binaries among UV-selected, hot subdwarf stars and population properties

Kawka, A. and Vennes, S. and O'Toole, S. and Nemeth, P. and Burton, D. and Kotze, E. and Buckle, D. A . H. (2015) New binaries among UV-selected, hot subdwarf stars and population properties. Monthly Notices of the Royal Astronomical Society, 450 (4). pp. 3514-3548. ISSN 0035-8711

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We have measured the orbital parameters of seven close binaries, including six new objects,in a radial velocity survey of 38 objects comprising a hot subdwarf star with orbital periods ranging from ∼0.17 to 3 d. One new system, GALEX J2205−3141, shows reflection on an M dwarf companion. Three other objects show significant short-period variations, but their orbital parameters could not be constrained. Two systems comprising a hot subdwarf paired
with a bright main-sequence/giant companion display short-period photometric variations possibly due to irradiation or stellar activity and are also short-period candidates. All except two candidates were drawn from a selection of subluminous stars in the Galaxy Evolution Explorer
ultraviolet sky survey. Our new identifications also include a low-mass subdwarf B star and likely progenitor of a low-mass white dwarf (GALEX J0805−1058) paired with an
unseen, possibly substellar, companion. The mass functions of the newly identified binaries imply minimum secondary masses ranging from 0.03 to 0.39M �. Photometric time series suggest that, apart from GALEX J0805−1058 and J2205
−3141, the companions are most likely white dwarfs. We update the binary population statistics: close to 40 per cent of hot subdwarfs have a companion.Also,we found that the secondary mass distribution shows a low-mass peak attributed to late-type dwarfs, and a higher mass peak and tail distribution attributed to white dwarfs and a few spectroscopic composites. Also, we found that the population
kinematics imply an old age and include a few likely halo population members.

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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Additional Information: Access to Published version in accordance with the copyright policy of the publisher.
Faculty / Department / School: Current - Faculty of Health, Engineering and Sciences - School of Agricultural, Computational and Environmental Sciences
Date Deposited: 27 Apr 2016 23:47
Last Modified: 01 Jul 2016 03:20
Uncontrolled Keywords: binaries: close; binaries: spectroscopic; subdwarfs; white dwarfs; ultraviolet: stars
Fields of Research : 02 Physical Sciences > 0201 Astronomical and Space Sciences > 020110 Stellar Astronomy and Planetary Systems
Socio-Economic Objective: E Expanding Knowledge > 97 Expanding Knowledge > 970102 Expanding Knowledge in the Physical Sciences
Identification Number or DOI: 10.1093/mnras/stv821

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