EDP Sciences
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Volume 399, Number 1, February III 2003
Page(s) 211 - 218
Section Stellar atmospheres
DOI http://dx.doi.org/10.1051/0004-6361:20021578

A&A 399, 211-218 (2003)
DOI: 10.1051/0004-6361:20021578

Understanding the LMXB X2127+119 in M 15

II. The UV data
Z. Ioannou1, 2, L. van Zyl3, T. Naylor1, 4, P. A. Charles5, B. Margon6, L. Koch-Miramond7 and S. Ilovaisky8

1  Department of Physics, Keele University, Keele, Staffordshire, ST5 5BG, UK
2  Department of Astronomy, University of Texas at Austin, C-1400, Austin, TX 78712, USA
3  Department of Astrophysics, Oxford University, Nuclear Physics Lab., Keeble Road, Oxford, OX1 3RH, UK
4  School of Physics, University of Exeter, Stocker Road, Exeter, EX4 4QL, UK
5  Department of Physics and Astronomy, University of Southampton, Southampton, SO17 1BJ, UK
6  Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
7  Service d'Astrophysique, DSM/DAPNIA/SAp, CE Saclay, 91191 Gif-sur-Yvette Cedex, France
8  Observatoire de Haute-Provence, 04870, Saint-Michel-l'Observatoire, France

(Received 20 November 2001 / Accepted 30 October 2002 )

We present HST UV observations of the high-inclination low mass X-ray binary AC211 (X2127+119), which is located in the globular cluster M 15 (NGC 7078). We have discovered a CIV P Cygni profile in this system, which confirms the existence of an outflow from AC211. The outflow velocity as measured from the P Cygni profile is ${\simeq}1500$ km s -1. We calculate that the mass lost through this wind is too small to support a large period derivative as favoured by Homer & Charles (1998). Using new X-ray observations we have revised the ephemeris for AC211 and we find no evidence in support of a period derivative. The UV spectrum exhibits several absorption features due to O, Si and C. The very strong HeII line at 1640 Å is not seen to modulate strongly with orbital phase, suggesting its origin lies in the outer parts of the system. In contrast, the eclipse of the UV continuum is short compared with the X-ray and optical eclipses.

Key words: accretion, accretion discs -- stars: binaries: eclipsing -- stars: coronae -- stars: individual: X2127+119, AC211 -- ultraviolet: stars

Offprint request: Z. Ioannou, zac@astro.as.utexas.edu

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