Astron. Astrophys. 348, 512-518 (1999)

On outflowing viscous disc models for Be stars

John M. Porter

Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead L41 1LD, UK (jmp@astro.livjm.ac.uk)

Received 19 March 1999 / Accepted 21 June 1999

Abstract

It is assumed that Be star discs are driven by viscosity. Emission from disc models is calculated and is confronted with continuum observations. It is found that the outflowing viscous disc models can reproduce the observed IR continuum emission. However, to exist as outflowing discs, either the discs are significantly acted upon by the stellar radiation field and/or there is significant cooling with radius in the disc. The energy generated via viscous dissipation is calculated and shown to play only a minor rôle in the energy balance of the disc.

A scenario whereby a B star may change into a Be star (and vice versa) by generating (reaccreting) the disc is suggested.

Key words: stars: circumstellar matter stars: emission-line, Be stars: mass-loss stars: rotation

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Contents

• 1. Introduction
• 2. Can outflowing viscous discs exist?
  • 2.1. Viscous discs
  • 2.2. Angular momentum transport in a viscous disc
  • 2.3. Inflow or outflow?
  • 2.4. Confrontation with observations
  • 2.5. Accretion discs?
• 3. Energy balance within the disc
  • 3.1. Liberation of energy via viscous dissipation
  • 3.2. IR free-free and free-bound emission
  • 3.3. How important is the viscous luminosity?
• 4. A case study - -Oph
  • 4.1. IR continuum excess fits
  • 4.2. Viscous luminosity versus free-free & free-bound emission
• 5. Discussion
• 6. Conclusion
• Acknowledgements
• References

© European Southern Observatory (ESO) 1999

Online publication: July 26, 1999
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