Astron. Astrophys. 359, 695-706 (2000)

The radiation driven winds of rotating B[e] supergiants

I. Pelupessy ¹, H.J.G.L.M. Lamers ^1,2 and J.S. Vink <sup>1

1</sup> Astronomical Institute, University of Utrecht, Princetonplein 5, 3584 CC Utrecht, The Netherlands (f.i.pelupessy@phys.uu.nl; lamers,j.s.vink@astro.uu.nl)
² SRON Laboratory for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands

Received 9 February 2000 / Accepted 26 April 2000

Abstract

We have formulated the momentum equation for sectorial line driven winds from rotating stars including: (a) the oblateness of the star, (b) gravity darkening (von Zeipel effect), (c) conservation of angular momentum, (d) line driving specified by the force multiplier parameters (k, , ), (e) finite disk correction factors for an oblate star with gravity darkening for both the continuum and the line driving. The equations are solved numerically. We calculated the distribution of the mass flux and the wind velocity from the pole to the equator for the winds of B[e]-supergiants. Rotation decreases the terminal velocity in the equatorial region but hardly affects the wind velocity from the poles; it enhances the mass flux from the poles while the mass flux from the equator remains nearly the same. These effects increase with increasing rotation rates.

We also calculated models with a bi-stability jump around 25 000 K, using force multipliers recently calculated with a Monte Carlo technique. In this case the mass flux increases drastically from the pole to the equator and the terminal velocity decreases drastically from pole to equator. This produces a density contrast in the wind of about a factor 10 independent of the rotation rate of the star. We suggest that the observed density contrast of a factor of the disks of B[e] stars may be reached by taking into account the wind compression due to the trajectories of the gas above the critical point towards the equatorial plane.

Key words: stars: early-type stars: emission-line, Be stars: mass-loss stars: rotation stars: supergiants stars: winds, outflows

Send offprint requests to: H.J.G.L.M. Lamers

Correspondence to: Astronomical Intitute, Princetonplein 5, 3584 CC Utrecht, The Netherlands

This article contains no SIMBAD objects.

Contents

• 1. Introduction
• 2. Theoretical context
• 3. The physics of rotation
  • 3.1. The shape of a rotating star
  • 3.2. Von Zeipel gravity darkening
  • 3.3. The equation of motion of a line driven wind of a rotating star
  • 3.4. The radiative line forces
• 4. Solutions of the equation of motion
  • 4.1. Simplified solutions for non-rotating star
    • 4.1.1. The point source approximation
    • 4.1.2. Simple finite disk correction
  • 4.2. Solution of the equation of motion for the wind of a rotating star
  • 4.3. The calculation of (r) and the continuum correction factor
  • 4.4. Solving the equation of motion
• 5. Application to B[e] winds
  • 5.1. A typical B[e] supergiant
  • 5.2. The overall density properties
  • 5.3. Varying
• 6. Rotationally induced bi-stability models
• 7. Summary and discussion
• References

© European Southern Observatory (ESO) 2000

Online publication: July 7, 2000
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