S. Otero

THE FIRST DETERMINATION OF THE VISCOSITY PARAMETER IN THE CIRCUMSTELLAR DISK OF A Be STAR

Be stars possess gaseous circumstellar decretion disks, which are well described using standard

Stellar and circumstellar activity of the Be star ω CMa I. Line and continuum emission in 1996-2002

\alpha

The yellow hypergiant HR 5171 A: Resolving a massive interacting binary in the common envelope phase

-disk theory. The Be star 28 CMa recently underwent a long outburst followed by a long period of quiescence, during which the disk dissipated. Here we present the first time-dependent models of the dissipation of a viscous decretion disk. By modeling the rate of decline of the V-band excess, we determine that the viscosity parameter

A search for photometric variability in magnetic chemically peculiar stars using ASAS-3 data

\alpha=1.0\pm0.2

The ASAS-SN catalogue of variable stars I: The Serendipitous Survey

, corresponding to a mass injection rate

The 2008+ outburst of the Be star 28 CMa - a multi-instrument study

\dot{M}=(3.5\pm 1.3) \times 10^{-8}\ M_\sun\,\mathrm{yr}^{-1}

An investigation of the photometric variability of confirmed and candidate Galactic Be stars using ASAS-3 data

. Such a large value of

The life cycles of Be viscous decretion discs: The case of ω CMa

\alpha

Interacting binaries W Serpentids and double periodic variables

suggests that the origin of the turbulent viscosity is an instability in the disk whose growth is limited by shock dissipation. The mass injection rate is more than an order of magnitude larger than the wind mass loss rate inferred from UV observations, implying that the mass injection mechanism most likely is not the stellar wind, but some other mechanism.

Modeling the Complete Lightcurve of omega CMa

Echelle spectroscopy and mostly unaided-eye photometry of the southern Be star ω CMa were obtained in the period 1996-2003. The monitoring is bracketed by two brightenings by 0. m 4-0. m 5. The results of a literature search suggest that such phases occur about once a decade and have various commonalities. Along with these photometric events goes enhanced line emission. This is due to an increased total mass of the disk as well as to a change in its density profile. The models by Poeckert & Marlborough (1978, 1979) imply that the enhanced continuum flux originates from the inner disk. Higher-order Balmer line emission is correlated with brightness. The increase in Hα is retarded by some months, possibly indicating a time delay in filling up and ionizing the outer disk. In the (U − B) vs. (B −V) colour diagram and the D54 vs. D34 Balmer decrement diagram the path from the ground to the bright state is distinct from the return path. This could result from the bulk of the disk matter being in the outer (inner) disk during the photometric ground (high) state, while the two transitions between the two states are both due to changes progressing radially outward. Some µ Cen-like outbursts (Rivinius et al. 1998c) seem to occur in all phases. It is conceivable that the build-up of the inner disk is caused by more frequent or more effective outbursts. During the photometric bright state various other phenomena gain in prominence and suggest this to be a phase of increased activity. Of particular interest, but possibly only apparently related to this phase, are absorption components at redshifts well beyond the range covered by the combination of rotation and nonradial pulsation.