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The Be/X-ray transient 4U 0115+63/V635 Cassiopeiae. II. Outburst mechanisms

The Be/X-ray transient 4U 0115+63/V635 Cassiopeiae. II. Outburst mechanisms
The Be/X-ray transient 4U 0115+63/V635 Cassiopeiae. II. Outburst mechanisms
We present multi-wavelength long-term monitoring observations of V635 Cas, the optical counterpart to the transient X-ray pulsar 4U 0115+63. The evolution of emission lines and photometric magnitudes indicates that the Be star undergoes relatively fast ( ~ 3-5 \: yr) quasi-cyclic activity, losing and reforming its circumstellar disc. We show that the general optical, infrared and X-ray behaviour can be explained by the dynamical evolution of the viscous circumstellar disc around the Be star. After each disc-loss episode, the disc starts reforming and grows until it reaches the radius at which the resonant interaction of the neutron star truncates it. At some point, the disc becomes unstable to (presumably radiative) warping and then tilts and starts precessing. The tilting is very large and disc precession leads to a succession of single-peaked and shell profiles in the emission lines. Type II X-ray outbursts take place after the disc has been strongly disturbed and we speculate that the distortion of the disc leads to interaction with the orbiting neutron star. We discuss the implications of these correlated optical/X-ray variations for the different models proposed to explain the occurrence of X-ray outbursts in Be/X-ray binaries. We show that the hypothesis of mass ejection events as the cause of the spectacular variability and the X-ray outbursts is unlikely to be meaningful for any Be/X-ray binary.
stars, circumstellar matter, stars: emission-line Be, stars: individual 4U 0115+63, binaries: close, stars: neutron, x-ray: stars
117-131
Negueruela, I.
9d1fc407-8ec5-43db-a49f-ce5b2c05e9b7
Okazaki, A.T.
4e544762-b768-4039-b381-166f4b8e3f3f
Fabregat, U.
668e898e-3815-45db-a06f-180adb391f54
Coe, M.J.
04dfb23b-1456-46a3-9242-5cee983471d5
Munari, U.
5129ec9e-ce1d-4372-b655-caa82c983000
Tomov, T.
15acd12c-4a70-4ddf-a4e3-74459595ed45
Negueruela, I.
9d1fc407-8ec5-43db-a49f-ce5b2c05e9b7
Okazaki, A.T.
4e544762-b768-4039-b381-166f4b8e3f3f
Fabregat, U.
668e898e-3815-45db-a06f-180adb391f54
Coe, M.J.
04dfb23b-1456-46a3-9242-5cee983471d5
Munari, U.
5129ec9e-ce1d-4372-b655-caa82c983000
Tomov, T.
15acd12c-4a70-4ddf-a4e3-74459595ed45

Negueruela, I., Okazaki, A.T., Fabregat, U., Coe, M.J., Munari, U. and Tomov, T. (2001) The Be/X-ray transient 4U 0115+63/V635 Cassiopeiae. II. Outburst mechanisms. Astronomy & Astrophysics, 369 (2001), 117-131. (doi:10.1051/0004-6361:20010077).

Record type: Article

Abstract

We present multi-wavelength long-term monitoring observations of V635 Cas, the optical counterpart to the transient X-ray pulsar 4U 0115+63. The evolution of emission lines and photometric magnitudes indicates that the Be star undergoes relatively fast ( ~ 3-5 \: yr) quasi-cyclic activity, losing and reforming its circumstellar disc. We show that the general optical, infrared and X-ray behaviour can be explained by the dynamical evolution of the viscous circumstellar disc around the Be star. After each disc-loss episode, the disc starts reforming and grows until it reaches the radius at which the resonant interaction of the neutron star truncates it. At some point, the disc becomes unstable to (presumably radiative) warping and then tilts and starts precessing. The tilting is very large and disc precession leads to a succession of single-peaked and shell profiles in the emission lines. Type II X-ray outbursts take place after the disc has been strongly disturbed and we speculate that the distortion of the disc leads to interaction with the orbiting neutron star. We discuss the implications of these correlated optical/X-ray variations for the different models proposed to explain the occurrence of X-ray outbursts in Be/X-ray binaries. We show that the hypothesis of mass ejection events as the cause of the spectacular variability and the X-ray outbursts is unlikely to be meaningful for any Be/X-ray binary.

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More information

Published date: 2001
Keywords: stars, circumstellar matter, stars: emission-line Be, stars: individual 4U 0115+63, binaries: close, stars: neutron, x-ray: stars

Identifiers

Local EPrints ID: 37651
URI: http://eprints.soton.ac.uk/id/eprint/37651
PURE UUID: df79bf75-790c-4cd8-9d5e-3742cf66d6de
ORCID for M.J. Coe: ORCID iD orcid.org/0000-0002-0763-8547

Catalogue record

Date deposited: 25 May 2006
Last modified: 16 Mar 2024 02:35

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Contributors

Author: I. Negueruela
Author: A.T. Okazaki
Author: U. Fabregat
Author: M.J. Coe ORCID iD
Author: U. Munari
Author: T. Tomov

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