Astron. Astrophys. 359, 1075-1084 (2000)

Line formation in Be star circumstellar disks ^* **

Shear broadening, shell absorption, stellar obscuration and rotational parameter

W. Hummel ¹ and M. Vrancken <sup>2

1</sup> Institut für Astronomie und Astrophysik und Universitätssternwarte München, Scheinerstrasse 1, 81673 München, Germany
² Royal Observatory of Belgium, Ringlaan 3, 1180 Brussel, Belgium

Received 29 March 1999 / Accepted 28 April 2000

Abstract

We improve the theory of Horne & Marsh on shear broadening in accretion disks of CVs and adapt it to Be star circumstellar disks. Stellar obscuration and shell absorption are taken into account in detail. It is shown that shell absorption is already present in those emission lines where the central depression does not drop below the stellar continuum. The model profiles are fitted to observed symmetric H net emission lines with low equivalent width. The derived disk radii range from to and the surface emissivity varies as with . The comparison between model profiles of rotational parameter with the optically thick H profile of HR 5440 rules out the range of . This can be understood by the lack of velocity shear in the outer disk regions. We conclude that Keplerian rotation () is a valid approximation.

Key words: line: formation line: profiles stars: circumstellar matter stars: emission-line, Be

* Based on observations collected at the German-Spanish Astronomical Center (DSAZ), Calar Alto, operated by the Max-Plank-Institut für Astronomie Heidelberg jointly with the Spanish National Commission for Astronomy
** Based on observations collected at the Observatoire de Haute-Provence (OHP), CNRS, France

Send offprint requests to: W. Hummel

Correspondence to: hummel@usm.uni-muenchen.de

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Contents

• 1. Introduction
• 2. Basic model assumptions and equations
  • 2.1. Shear broadening
  • 2.2. Stellar obscuration and shell absorption
  • 2.3. Large inclination effects
  • 2.4. Test calculation for pure shell profiles
• 3. Model line profiles
  • 3.1. Shear broadening
  • 3.2. Stellar obscuration
  • 3.3. Shell absorption
• 4. Application to observed H emission lines
  • 4.1. Observations
  • 4.2. Subtraction of the underlying stellar absorption profile
  • 4.3. Fitting procedure for net emission profiles
• 5. Circular velocity law
• 6. Discussion
• 7. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 2000

Online publication: July 13, 2000
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