On the ultracompact nature of 4U 1822−000

Authors: Shahbaz, T.; Watson, C. A.¹; Hernandez-Peralta, H.²

Source: Monthly Notices of the Royal Astronomical Society, Volume 376, Number 4, April 2007 , pp. 1886-1888(3)

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Abstract:

We report the discovery of a periodic modulation in the optical lightcurve of the candidate ultracompact X-ray binary 4U 1822−000. Using time-resolved optical photometry taken with the William Herschel Telescope we find evidence for a sinusoidal modulation with a semi-amplitude of 8 per cent and a period of 191 min, which is most likely close to the true orbital period of the binary. Using the van Paradijs & McClintock relation for the absolute magnitude and the distance modulus allowing for interstellar reddening, we estimate the distance to 4U 1822−000 to be 6.3 kpc. The long orbital period casts severe doubts on the ultracompact nature of 4U 1822−000.

Keywords: accretion, accretion discs; binaries: close; stars: individual: 4U 1822−000

Document Type: Research article

DOI: http://dx.doi.org/10.1111/j.1365-2966.2007.11579.x

Affiliations: 1: Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH 2: Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain

Publication date: 2007-04-01