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Astron. Astrophys. 321, 477-484 (1997)

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Spectroscopic study of GRO J1655-40: the outburst and the decline *

A. Bianchini 1, M. Della Valle 1, N. Masetti 1 and R. Margoni 2

1 Dipartimento di Astronomia, Università di Padova, vicolo dell'Osservatorio, 5, I-35122 Padua, Italy
2 Osservatorio Astrofisico di Asiago, via dell'Osservatorio Astrofisico, 8, I-36012 Asiago, Italy

Received 2 July 1996 / Accepted 24 September 1996

Abstract

We have analysed 53 optical spectra (40 taken during the outburst peak and 13 during the decline) of the Soft X-ray Transient GRO J1655-40 (=X-Ray Nova Scorpii 1994). The [FORMULA] flux during outburst shows a periodicity of 1.3 days, which is almost exactly one half of the one obtained by Bailyn et al. (1995b) from radial velocity variations. A possible explanation for this behaviour is provided. We also notice that the spectral emission features shrink or turn into absorption lines with an emission core during the decline. This is typical of Soft X-ray Transients and suggests that an expansion of the disk takes place after the outburst peak phase.

Key words: accretion disks – stars: individual (GRO J1655-40, X – ray Nova Sco 1994) – X – rays: stars

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

Send offprint requests to: N. Masetti, masetti@astrpd.pd.astro.it

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© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998
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