Free access article

A&A 400, 655-658 (2003)
DOI: 10.1051/0004-6361:20030017

Near IR spectroscopy of the X-ray binary Circinus X-1

J. S. Clark¹, P. A. Charles², W. I. Clarkson² and M. J. Coe<sup>2

1</sup>  Department of Physics and Astronomy, University College London, Gower Street, London, WC1E 6BT, UK
²  Department of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ, UK

(Received 5 December 2002 / Accepted 6 January 2003 )

Abstract
We report on new K band spectroscopy of the X-ray binary Cir X-1 , which reveals the spectrum to be dominated by emission from H I, He I and low-excitation metals. No features of photospheric origin are identifiable in the spectrum, preventing an unambiguous classification of the mass donor within the system. While the spectrum superficially resembles that of a high-luminosity mid-B supergiant we consider that the magnitude and timescale of the photometric and spectroscopic variability renders such an identification highly unlikely. Instead we favour an explanation where the spectrum is dominated by emission from an accretion disc and/or accretion driven outflow(s), hence obscuring the spectrum of the underlying star.

Key words: stars: binaries: general -- infrared: stars -- stars: Individual: Cir X-1

Offprint request: J. S. Clark, jsc@star.ucl.ac.uk

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© ESO 2003

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