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Astron. Astrophys. 329, 538-550 (1998)

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The quiescence optical light curve of Nova Scorpii 1994 (=GRO J1655-40) *

F. van der Hooft 1, M.H.M. Heemskerk 1, F. Alberts 1 and J. van Paradijs 1, 2

1 Astronomical Institute "Anton Pannekoek", University of Amsterdam and Center for High Energy Astrophysics, Kruislaan 403,
1098 SJ Amsterdam, The Netherlands
2 Department of Physics, University of Alabama in Huntsville, Huntsville, AL 35899, USA

Received 20 March 1997 / Accepted 8 August 1997


We report on extensive V, R, and i band photometry of the black-hole candidate Nova Sco 1994 (GRO J1655-40) obtained during March 1996, when the source was close to its quiescent pre-outburst optical brightness (V =17.3). From our observations and data taken from the literature we derive a refined ephemeris for inferior conjunction of the secondary star: HJD [FORMULA]. We have modeled the V, R, and i band light curves in terms of a Roche lobe filling secondary and an accretion disk around the compact star, the latter described as a flat cylinder with a radial temperature distribution. From the shape of the light curve we constrain the binary inclination and mass of the secondary star to lie in the ranges [FORMULA] - [FORMULA] and 1.60-3.10 M [FORMULA], respectively. This limits the mass of the black-hole to the range 6.29-7.60 M [FORMULA]. The mass range we obtained for the secondary star is supported by the results of stellar evolution calculations.

Key words: stars: binaries: close – individual: Nova Sco 1994 (GRO J1655 – 40) – X-rays: stars

* Based on observations made at the European Southern Observatory, La Silla, Chile

Send offprint requests to: F. van der Hooft

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© European Southern Observatory (ESO) 1998

Online publication: December 8, 1997