Negueruela, IgnacioIgnacioNegueruelaOkazaki, A. T.A. T.Okazaki2020-09-172020-09-172001-04-01https://hdl.handle.net/20.500.13025/20Astronomy and Astrophysics, v.369, p.108-116 (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.enstars: circumstellae matterstars emission-lineBestars: individual: 4U 0115+63binaries: closestars: neutronX-ray: starsjournal article10.1051/0004-6361 20010146http://adsabs.harvard.edu/abs/2001A&A...369..108Nhttps://www.aanda.org/component/article?access=bibcode&bibcode=&bibcode=2001A%2526A...369..108NFUL2001A&A...369..108N