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

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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 1

1 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


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 [FORMULA] km s-1. By measuring the width of the H [FORMULA] emission line profile of the accretion disc, we estimate the binary inclination to [FORMULA] and also estimate the semi-amplitude of the companion star's radial velocity curve to be [FORMULA] 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)

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© European Southern Observatory (ESO) 1997

Online publication: April 20, 1998