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Astron. Astrophys. 341, 491-498 (1999)


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Keck observations of the black-hole candidate GRO J0422+32 *

E. Harlaftis 1, S. Collier 1, K. Horne 1 and A.V. Filippenko 2

1 School of Physics and Astronomy, University of St. Andrews, KY16 9SS, UK (e-mail: ehh@astro.noa.gr; sjc2@st-and.ac.uk; kdh1@st-andrews.ac.uk)
2 Department of Astronomy, University of California, Berkeley, CA 94720-3411, USA (e-mail: alex@astro.berkeley.edu)

Received 10 August 1998 / Accepted 21 October 1998

Abstract

Keck observations of the black-hole candidate GRO J0422+32 in quiescence have been used by Filippenko, Matheson, & Ho (1995) to determine a mass function [FORMULA] for the compact object. Reanalysis of the data shows that the mass ratio, [FORMULA], is [FORMULA] from the rotational broadening of the companion star [FORMULA] km s-1 ([FORMULA]). From q and the mass function (slightly revised to [FORMULA]), we derive the mass of the compact object, [FORMULA]. The companion star (M2[FORMULA] spectral type) contributes [FORMULA]% of the light at red wavelengths. An H[FORMULA] Doppler image of the system shows the typical ring-like distribution of an accretion disk. Emissivity laws for H[FORMULA] in black-hole binaries roughly follow an [FORMULA] law, which is also supported by GRO J0422+32. The Li I [FORMULA]6708 absorption line is not detected ([FORMULA] equivalent width limit of 0.13 Å), in contrast to four other X-ray binaries.

Key words: black hole physics – stars: binaries: close – stars: individual: GRO J0422+32 – stars: novae, cataclysmic variables – X-rays: stars

* Based on observations obtained at the W.M. Keck Observatory

Present address: Astronomical Institute, National Observatory of Athens, Lofos Nymfon, P.O. Box 20048, Athens 11810, Greece

Send offprint requests to: E. Harlaftis

© European Southern Observatory (ESO) 1999

Online publication: December 4, 1998

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