We analyzed V -band photometry of the Be star \omega CMa , obtained during the last four decades , during which the star went through four complete cycles of disc formation and dissipation .
The data were simulated by hydrodynamic models based on a time-dependent implementation of the viscous decretion disc ( VDD ) paradigm , in which a disc around a fast-spinning Be star is formed by material ejected by the star and driven to progressively larger orbits by means of viscous torques .
Our simulations offer a good description of the photometric variability during phases of disc formation and dissipation , which suggests that the VDD model adequately describes the structural evolution of the disc .
Furthermore , our analysis allowed us to determine the viscosity parameter \alpha , as well as the net mass and angular momentum ( AM ) loss rates .
We find that \alpha is variable , ranging from 0.1 to 1.0 , not only from cycle to cycle but also within a given cycle .
Additionally , build-up phases usually have larger values of \alpha than the dissipation phases .
Furthermore , during dissipation the outward AM flux is not necessarily zero , meaning that \omega CMa does not experience a true quiescence but , instead , switches between a high to a low AM loss rate during which the disc quickly assumes an overall lower density but never zero .
We confront the average AM loss rate with predictions from stellar evolution models for fast-rotating stars , and find that our measurements are smaller by more than one order of magnitude .