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Krtička, M.; Lipták, J.; Materna, J.; Štěrba, F.; Štěrbová, J.; Vrzal, J.; Wintrová, M.

doi:10.1023/a:1024653525657

Cited by 6 publications

(1 citation statement)

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“…The system of three hydrodynamic equations (continuity equation, equations of stationary conservation of R and φ components of momentum) is numerically approximated by differentiation at selected radial grid points with the use of the Newton-Raphson method (Krtička 2003).…”

Section: Numerical Approachmentioning

confidence: 99%

Hydrodynamics of Decretion Disks of Rapidly Rotating Stars

Kurfürst¹

2011

Proc. IAU

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Abstract. During the evolution of hot stars, the equatorial rotational velocity can approach its critical value. Further increase in rotation rate is not allowed, consequently mass and angular momentum loss is needed to keep the star near and below its critical rotation. The matter ejected from the equatorial surface forms the outflowing viscous decretion disk. Models of outflowing disks of hot stars have not yet been elaborated in detail, although it is clear that such disks can significantly influence the evolution of rapidly rotating stars. One of the most important features is the disk radial temperature variation because the results will help us to specify the mass and angular momentum loss of rotating stars via decretion disks.Keywords. Rotation, mass loss, hydrodynamics Basic theoretical considerationsIn contrast to the usual stellar wind mass loss we study the role of mass loss via an equatorial outflowing viscous decretion disk evolution in massive stars (Krtička et al. 2011). Evolutionary contraction brings massive star to critical rotation: it leads to the formation of the disk. Further increase in rotation rate is not allowed (Ω = 0), net loss of angular momentum is given byL =İΩ crit , where Ω crit = GM/R 3 eq is the critical rotation frequency. The viscous coupling in a decretion disk can transport angular momentum outward to some outer disk radius, R out . When a Keplerian disk is present, in comparison with the case where mass decouples in a spherical shell just at the surface of the star, the mass loss is then reduced by a factorKey point of the analysis: the angular momentum loss from the decretion disk can greatly exceed the angular momentum loss from the stellar wind outflow. Numerical approachFor the numerical modelling, it is necessary to solve the system of hydrodynamic equations in cylindrical coordinates (Krtička et al. 2011). Except for the mass conservation (continuity) equation, we have to include the equations for stationary conservation of R and φ components of momentum, supplemented by appropriate boundary conditions.For further calculations, the Shakura-Sunyaev α viscosity parameter is introduced (Shakura & Sunyaev 1973); it expresses the quantityṽ/a (somewhat simplified since there are also effects of the magnetic field), where a is the sound speed (a 2 = kT /µm H ) and we have v R (R crit ) = a.The temperature distribution in the radial direction is assumed as T = T 0 (R eq /r) p , where p is a free parameter (power law). Some of recent models (e.g. Carcioffi et al.

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Section: Numerical Approachmentioning

confidence: 99%