Revisiting Viscous Transonic Decretion Disks of Be Stars

Abstract

In the context of Be stars, we restudied the viscous transonic decretion disk model of these stars. This model is driven by a radiative force due to an ensemble of optically-thin lines and viscosity considering the Shakura Sunyaev prescription. The non-linear equation of motion presents a singularity (sonic point) and an eigenvalue, which is also the initial condition at the stellar surface. Then, to obtain this eigenvalue, we set it as a radial quantity and perform a detailed topological analysis. Thereafter, we describe a numerical method for solving either Nodal and Saddle transonic solutions. The value of the viscosity,"alpha", barely determine the location of the sonic point, but it determines the topology of the solution. We found two Nodal solutions, which are almost indistinguishable between them. Saddle solutions are founded for lower values of "alpha" than the required of the Nodal solutions. In addition, rotational velocity do not play a determine role in the velocity (and density) profile, because viscosity effects collapse all the solutions to almost a unique one in a small region above the stellar surface. A suitable combination of line force parameters and/or disk temperature, give location of the sonic point lower than 50 stellar radii, describing a truncated disk. This could explain the SED turndown observed in Be stars without needing a binary companion.

arXiv commentAccepted in A&A

References in corpus (16)

• Classical Be Stars: Rapidly Rotating B Stars with Viscous Keplerian Decretion Disks
• NLTE Monte Carlo Radiative Transfer: I. The Thermal Properties of Keplerian Disks around Classical Be Stars
• Viscous Transonic Decretion in Disks of Be Stars
• Dynamical Evolution of Viscous Disks around Be Stars. I: photometry
• The Thermal Structure of the Circumstellar Disk Surrounding the Classical Be Star gamma Cassiopeia
• Mass and angular momentum loss via decretion disks
• The life cycles of Be viscous decretion discs: fundamental disc parameters of 54 SMC Be stars
• The influence of rotation in radiation driven wind from hot stars: New solutions and disk formation in Be stars
• First spectro-interferometric survey of Be stars I. Observations and constraints on the disks geometry and kinematics
• Revealing the structure of the outer disks of Be stars
• Line-driven ablation of circumstellar disks: I. Optically thin decretion disks of classical Oe/Be stars
• Time-dependent modeling of extended thin decretion disks of critically rotating stars
• The influence of rotation in radiation driven winds from hot stars II. CAK topological analysis
• Line-driven ablation of circumstellar discs: IV. The role of disc ablation in massive star formation and its contribution to the stellar upper mass limit
• Line-driven ablation of circumstellar discs: III. Accounting for and analyzing the effects of continuum optical depth
• A New Numerical Method for Solving Radiation Driven Winds from Hot Stars