Large-scale perturbations in the circumstellar envelopes of Be/X-ray binaries

Abstract

We investigate the spectroscopic characteristics of the optical components of Be/X-ray binary systems, using data collected during our seven-year monitoring campaign. We find examples of major changes in the emission line profiles associated with Type II X-ray outbursts, later developing into V/R variability cycles. We show that the time-scales for V/R variability in Be/X-ray transients extend from a few weeks to years and interpret all these changes as due to the presence of global disruptions of the axisymmetric density distribution in the extended envelopes of the Be stars in these systems. The association between X-ray outbursts and V/R variability, the occurrence of very fast changes and the very short quasi-periods of variability displayed by Be/X-ray binaries lead us to conclude that the presence of the neutron star is an important factor affecting the dynamics of the disc-like envelopes. The interaction between the compact companion and the disc would explain the correlation between H-alpha strength and orbital period recently found. The characteristics of the V/R cycles are, however, mainly independent of the binary parameters.