Probing the properties of Be star discs with spectroastrometry and NLTE radiative transfer modelling: β CMi

Authors

  • H. E. Wheelwright,

    Corresponding author
    1. Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
    2. School of Physics & Astronomy, University of Leeds, Woodhouse Lane, Leeds LS2 9JT
      E-mail: hwheelwright@mpifr-bonn.mpg.de
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  • J. E. Bjorkman,

    1. Department of Physics & Astronomy, University of Toledo, MS111 2801 West Bancroft Street, Toledo, OH 43606, USA
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  • R. D. Oudmaijer,

    1. School of Physics & Astronomy, University of Leeds, Woodhouse Lane, Leeds LS2 9JT
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  • A. C. Carciofi,

    1. Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, Rua do Matão 1226, Cidade Universitária, 05508-900 São Paulo, Brazil
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  • K. S. Bjorkman,

    1. Department of Physics & Astronomy, University of Toledo, MS111 2801 West Bancroft Street, Toledo, OH 43606, USA
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  • J. M. Porter

    Corresponding author
    1. Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead CH41 1 LD
      Deceased.
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Based on observations conducted at the European Southern Observatory (ESO), Paranal, Chile as part of the programme 082.D-0140.

E-mail: hwheelwright@mpifr-bonn.mpg.de

Deceased.

ABSTRACT

While the presence of discs around classical Be stars is well established, their origin is still uncertain. To understand what processes result in the creation of these discs and how angular momentum is transported within them, their physical properties must be constrained. This requires comparing high spatial and spectral resolution data with detailed radiative transfer modelling. We present a high spectral resolution, R∼ 80 000, sub-milliarcsecond precision, spectroastrometric study of the circumstellar disc around the Be star β CMi. The data are confronted with 3D, non-local thermodynamic equilibrium radiative transfer calculations to directly constrain the properties of the disc. Furthermore, we compare the data to disc models featuring two velocity laws: Keplerian, the prediction of the viscous disc model, and angular momentum conserving rotation. It is shown that the observations of β CMi can only be reproduced using Keplerian rotation. The agreement between the model and the observed spectral energy distribution, polarization and spectroastrometric signature of β CMi confirms that the discs around Be stars are well modelled as viscous decretion discs.

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