Astron. Astrophys. 326, L5-L8 (1997)

Letter to the Editor

The rotation speed of the companion star in Aquila X-1

T. Shahbaz ¹, J. Casares ² and P.A. Charles <sup>1

1</sup> Department of Astrophysics, Oxford University, Keble Road, Oxford, OX1 3RH, UK
² Instituto de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain

Received 17 June 1997 / Accepted 22 July 1997

Abstract

We have obtained medium resolution spectra of the neutron star X-ray transient Aql X-1 during quiescence. We determine the spectral type of the companion star to be K1 and also estimate its rotation speed to be km s^-1. By measuring the width of the H emission line profile of the accretion disc, we estimate the binary inclination to and also estimate the semi-amplitude of the companion star's radial velocity curve to be 170 km s^-1.

Key words: binaries: general stars: fundamental parameters, stars: individual: Aql X 1 stars: neutron

Send offprint requests to: T. Shahbaz (tsh@astro.ox.ac.uk)

SIMBAD Objects

Contents

• 1. Introduction
• 2. Observations and data reduction
• 3. The spectral type and rotational broadening of the companion star
• 4. The Aql X-1 spectrum
• 5. Discussion
  • 5.1. The binary inclination
  • 5.2. The velocity
• 6. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1997

Online publication: April 20, 1998
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