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 [alpha]-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...

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Bibliographic Details
Published in:Astrophysical journal. Letters 2012-01, Vol.744 (1), p.L15-5
Main Authors: Carciofi, Alex C, Bjorkman, Jon E, Otero, Sebastián A, Okazaki, Atsuo T, Štefl, Stanislav, Rivinius, Thomas, Baade, Dietrich, Haubois, Xavier
Format: Article
Language:English
Subjects:
ASTROPHYSICS
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
Computational fluid dynamics
Disks
Dissipation
EMISSION
INSTABILITY
MASS
Mathematical models
STARS
STELLAR WINDS
TIME DEPENDENCE
TURBULENCE
VISCOSITY
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Summary:Be stars possess gaseous circumstellar decretion disks, which are well described using standard [alpha]-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 [alpha] = 1.0 + or - 0.2, corresponding to a mass injection rate M = (3.5 + or - 1.3) x 10 super(-8) M sub([sm circle in circle]) yr super(-1). Such a large value of [alpha] 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.
ISSN:2041-8205
2041-8213
DOI:10.1088/2041-8205/744/1/L15