Optical spectroscopy of the low-mass X-ray binary GX 9+9 |
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Authors: | R. Cornelisse D. Steeghs J. Casares P. A. Charles A. D. Barnes R. I. Hynes K. O'Brien |
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Affiliation: | Instituto de Astrofisica de Canarias, Via Lactea, La Laguna E-38200, Santa Cruz de Tenerife, Spain; School of Physics and Astronomy, University of Southampton, Highfield, Southampton SO17 1BJ; Harvard-Smithsonian Centre for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA; Department of Physics, University of Warwick, Coventry CV4 7AL; South Africa Astronomical Observatory, PO Box 9, Observatory 7935, South Africa; Department of Physics and Astronomy, 202 Nicholson Hall, Louisiana State University, Baton Rouge, LA 70803, USA; European Southern Observatory, Casilla 19001, Santiago 19, Chile |
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Abstract: | Phase-resolved medium-resolution VLT spectroscopy of the low-mass X-ray binary GX 9+9 has revealed narrow C iii emission lines that move in phase relative to our new estimate of the ephemeris, and show a velocity amplitude of 230 ± 35 km s−1. We identify the origin of these lines as coming from the surface of the donor star, thereby providing the first estimate of the mass function of f ( M 1) ≥ 0.22 M⊙ . Rotational broadening estimates together with assumptions for the mass donor give 0.07 ≤ q ≤ 0.35 and 182 ≤ K 2≤ 406 km s−1 . Despite a low-mass ratio, there is no evidence for a superhump in our data set. Doppler maps of GX 9+9 show the presence of a stream overflow, either in the form of material flowing downward along the accretion disc rim or in a similar fashion as occurs in high mass transfer rate cataclysmic variables known as the SW Sex stars. Finally, we note that the Bowen region in GX 9+9 is dominated by C iii instead of N iii emission as has been the case for most other X-ray binaries. |
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Keywords: | accretion, accretion discs stars: individual: GX 9+9 X-rays: binaries |
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