EDP Sciences
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Volume 369, Number 1, April I 2001
Page(s) 108 - 116
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20010146

A&A 369, 108-116 (2001)
DOI: 10.1051/0004-6361:20010146

The Be/X-ray transient 4U 0115+63/V635 Cassiopeiae

I. A consistent model
I. Negueruela1, 2 and A. T. Okazaki3

1  SAX SDC, ASI, c/o Nuova Telespazio, via Corcolle 19, 00131 Rome, Italy
2  Astrophysics Research Institute, Liverpool John Moores University, Byrom St., Liverpool L3 3AF, UK
3  Faculty of Engineering, Hokkai-Gakuen University, Toyohira-ku, Sapporo 062-8605, Japan

(Received 22 July 1999 / Accepted 10 January 2001 )

We present photometry and high SNR spectroscopy in the classification region of V635 Cas, the optical counterpart to the transient X-ray pulsar 4U 0115+63, taken at a time when the circumstellar envelope had disappeared. V635 Cas is classified as a B0.2Ve star at a distance of 7-8 kpc. We use the physical parameters derived from these observations and the orbit derived from X-ray observations to elaborate a model of the system based on the theory of decretion discs around Be stars. We show that the disc surrounding the Be star is truncated by the tidal/resonant interaction with the neutron star and cannot be in a steady state. This explains many of the observed properties of 4U 0115+63. In particular, because of this effect, under normal circumstances the neutron star cannot accrete from the disc, which explains the lack of regular type I outbursts from the source.

Key words: stars: circumstellar matter -- stars: emission-line, Be -- stars: individual: 4U 0115+63, -- binaries: close -- stars: neutron -- X-ray: stars

Offprint request: I. Negueruela, ignacio@astro.u-strasbg.fr

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