Volume 525, January 2011
|Number of page(s)||11|
|Section||Interstellar and circumstellar matter|
|Published online||29 November 2010|
Fast ray-tracing algorithm for circumstellar structures (FRACS)
Laboratoire H. Fizeau, UMR CNRS 6525, Université de Nice-Sophia Antipolis
(UNS), Observatoire de la Côte d’Azur (OCA),
Nice Cedex 2,
2 Observatório Nacional, Rua General José Cristino, 77, 20921-400 São Cristovão, Rio de Janeiro, Brazil
3 Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo (USP), Rua do Matão 1226, Cidade Universitária, São Paulo, SP - 05508-900, Brazil
4 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
5 Deutsches Zentrum für Luft- und Raumfahrt, Raumfahrt-Agentur, Königswinterer Strasse 522-524, 53227 Bonn, Germany
Received: 10 June 2010
Accepted: 15 September 2010
Context. B[e] supergiants are luminous, massive post-main sequence stars exhibiting non-spherical winds, forbidden lines, and hot dust in a disc-like structure. The physical properties of their rich and complex circumstellar environment (CSE) are not well understood, partly because these CSE cannot be easily resolved at the large distances found for B[e] supergiants (typically ≳1 kpc).
Aims. From mid-IR spectro-interferometric observations obtained with VLTI/MIDI we seek to resolve and study the CSE of the Galactic B[e] supergiant CPD-57° 2874.
Methods. For a physical interpretation of the observables (visibilities and spectrum) we use our ray-tracing radiative transfer code (FRACS), which is optimised for thermal spectro-interferometric observations.
Results. Thanks to the short computing time required by FRACS (<10 s per monochromatic model), best-fit parameters and uncertainties for several physical quantities of CPD-57° 2874 were obtained, such as inner dust radius, relative flux contribution of the central source and of the dusty CSE, dust temperature profile, and disc inclination.
Conclusions. The analysis of VLTI/MIDI data with FRACS allowed one of the first direct determinations of physical parameters of the dusty CSE of a B[e] supergiant based on interferometric data and using a full model-fitting approach. In a larger context, the study of B[e] supergiants is important for a deeper understanding of the complex structure and evolution of hot, massive stars.
Key words: stars: individual: CPD-57° 2874 / methods: observational / methods: numerical / techniques: high angular resolution / techniques: interferometric / stars: emission-line, Be
Based on VLTI/MIDI observations collected at the European Southern Observatory (ESO), Paranal, Chile under ESO Programmes 074.D-0101 and 078.D-0213. Also based on observations at the ESO 2.2-m telescope, La Silla, Chile, under agreement with the Observatório Nacional-MCT (Brazil).
© ESO, 2010
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