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Session 48 - New Insights on X-ray Binaries - II.
Oral session, Wednesday, June 11
North Main Hall C/D,
One of the main difficulties in the study of the mechanisms leading to X-ray outbursts in Be/X-ray transients is our lack of understanding of the dynamics of the circumstellar discs of the central Be stars. This is hampered any attempts to correlate the evolution of the sometimes very complex, fast varying profiles of emission lines observed in the optical range and the X-ray behaviour. Recently, however, new developments in the modelling of the circumstellar discs of Be stars have led to the emergence of a new picture in which the variability of the emission lines is caused by the propagation of density waves in the quasi-Keplerian discs. The idea that asymmetric line profiles are caused by non-axisymmetric density distributions in the discs is now generally accepted.
We present observations showing that, during a giant X-ray outburst of A\,0535+262 in February 1994, the H\alpha line profile displayed quick variability. The quasi-cyclic pattern of variability changed immediately after the outburst. Likewise, the H\alpha line profile of the optical component of 4U\,0115+634 was observed to undergo large variability at about the time of a giant outburst in December 1995. After the outburst, the source initiated a cycle of variability, similar to those seen in Be stars with propagating density waves in their discs. At the same time, the source displayed for the first time since it has been observed a series of `normal' outbursts. We present evidence of the frequent presence of density waves in the discs surrounding the primary components of Be/X-ray binaries and investigate their possible connection with X-ray outbursts.
