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A detection of the donor star of Aquila X-1 during its 2004 outburst?

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Cornelisse, R., Casares, J., Steeghs, D. (Danny), 1972-, Barnes, A. D., Charles, P. A., Hynes, R. I. and O'Brien, K.. (2007) A detection of the donor star of Aquila X-1 during its 2004 outburst? Monthly Notices of the Royal Astronomical Society, Vol.375 (No.4). pp. 1463-1470. ISSN 00358711

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Abstract

Phase-resolved high-resolution optical spectroscopy has revealed narrow N iii and He ii emission lines from the soft X-ray transient Aquila X-1 during its 2004 outburst that move as a function of the orbit consistent with the phasing of the donor star. Under the assumption that these lines come from the irradiated side of the donor star, we can constrain its K2 velocity to ≥247 ± 8 km s−1 and derive a mass function of f(M1) ≥ 1.23 ± 0.12 M⊙. Estimates for the rotational broadening based on the emission components suggest a possible massive neutron star of ≥1.6 M⊙ (at 95 per cent confidence). However, an updated ephemeris and additional high-resolution spectroscopy of Aql X-1 during a future outburst are warranted in order to confirm that the narrow lines indeed originate on the donor star surface, and reliably characterize the system parameters of this important X-ray binary. Spectra taken during the end of the outburst show that the morphology of the emission lines changed dramatically. No donor star signature was present anymore, while the presence of narrow low-velocity emission lines became clear, making Aql X-1 a member of the slowly growing class of low-velocity emission-line sources.

Item Type: Journal Article
Subjects: Q Science > QB Astronomy
Divisions: Faculty of Science > Physics
Library of Congress Subject Headings (LCSH): X-ray bursts, X-ray binaries
Journal or Publication Title: Monthly Notices of the Royal Astronomical Society
Publisher: Wiley
ISSN: 00358711
Official Date: 2007
Volume: Vol.375
Number: No.4
Page Range: pp. 1463-1470
Identification Number: 10.1111/j.1365-2966.2006.11409.x
Status: Peer Reviewed
Publication Status: Published
Access rights to Published version: Restricted or Subscription Access
Funder: European Union (EU), Spain. Ministerio de Ciencia e Innovación (MICINN), Smithsonian Astrophysical Observatory, United States. National Aeronautics and Space Administration (NASA)
Grant number: MEIFCT. 2005-024685 (EU), AYA2002-03570 (MICINN), NNG06GC05G (NASA)
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URI: http://wrap.warwick.ac.uk/id/eprint/48690

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