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Spectroscopic evidence for a 5.4 minute orbital period in HM Cancri

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Roelofs, Gijs H. A., Rau, Arne, Marsh, T. R., Steeghs, D. (Danny), 1972-, Groot, P. J. (Paul J.) and Nelemans, G.. (2010) Spectroscopic evidence for a 5.4 minute orbital period in HM Cancri. Astrophysical Journal Letters, Vol.711 (No.2). L138-L142. ISSN 2041-8205

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Official URL: http://dx.doi.org/10.1088/2041-8205/711/2/L138

Abstract

HM Cancri is a candidate ultracompact binary white dwarf with an apparent orbital period of only 5.4 minutes, as suggested by X-ray and optical light-curve modulations on that period, and by the absence of longer-period variability. In this Letter, we present Keck-I spectroscopy which shows clear modulation of the helium emission lines in both radial velocity and amplitude on the 5.4 minute period and no other. The data strongly suggest that the binary is emitting He I 4471 from the irradiated face of the cooler, less massive star, and He II 4686 from a ring around the more massive star. From their relative radial velocities, we measure a mass ratio q = 0.50 +/- 0.13. We conclude that the observed 5.4 minute period almost certainly represents the orbital period of an interacting binary white dwarf. We thus confirm that HM Cnc is the shortest period binary star known: a unique test for stellar evolution theory, and one of the strongest known sources of gravitational waves for LISA.

Item Type:	Journal Article
Subjects:	Q Science > QB Astronomy
Divisions:	Faculty of Science > Physics
Library of Congress Subject Headings (LCSH):	Double stars, White dwarf stars
Journal or Publication Title:	Astrophysical Journal Letters
Publisher:	IOP Publishing Ltd
ISSN:	2041-8205
Date:	10 March 2010
Volume:	Vol.711
Number:	No.2
Number of Pages:	5
Page Range:	L138-L142
Identification Number:	10.1088/2041-8205/711/2/L138
Status:	Peer Reviewed
Publication Status:	Published
Access rights to Published version:	Restricted or Subscription Access
Funder:	United States. National Aeronautics and Space Administration (NASA), W. M. Keck Foundation, Nederlandse Organisatie voor Wetenschappelijk Onderzoek [Netherlands Organisation for Scientific Research] (NWO)
Grant number:	680.50.0610 (NWO), NNX08AK66G (NASA)
Related URLs:	Other Repository
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URI:	http://wrap.warwick.ac.uk/id/eprint/6284