The evolved B[e] star HD 87643: observations and a radiation-driven disc wind model for B[e] stars |
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| Authors: | René D Oudmaijer Daniel Proga Janet E Drew & Dolf de Winter |
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| Institution: | Imperial College of Science, Technology and Medicine, Blackett Laboratory, Prince Consort Road, London, SW7 2BZ,;Dpto. Física Téorica C–XI, Facultad de Ciencias, Universidad Autónoma de Madrid, Cantoblanco, E–28049 Madrid, Spain,;Centro de Astrofísica de Universidade do Porto, Campo Alegre 823, 4150 Porto, Portugal |
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| Abstract: | New high-resolution spectroscopic and medium-resolution spectropolarimetric data of the Be] star HD 87643 are presented, complemented with optical broad- and narrow-band imaging. The spectrum of HD 87643 exhibits the hybrid characteristics well known to be representative of the group of Be] stars; a fast wind with an expansion velocity in excess of 1000 km s?1 is measured in the hydrogen and helium lines, while a slower component is traced by lower excitation lines and forbidden lines. Clues to the geometry of the rapidly expanding circumstellar shell are provided by the startling polarization changes across Hα. Comparison with published schematic calculations indicates that the polarizing material is located in a slowly rotating, expanding disc structure. A hydrodynamical model is then presented, the results of which are consistent with the original two-wind concept for Be] stars, and which exhibits kinematic properties that may well explain the observed spectral features in HD 87643. The model calculations use as input a B star undergoing mass loss, surrounded by an optically thick disc. The resulting configuration consists of a fast polar wind from the star and a slowly expanding disc wind. The model also predicts that the stellar wind at intermediate latitudes is slower and denser than in the polar region. |
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| Keywords: | hydrodynamics polarization circumstellar matter stars: emission-line Be stars: individual: HD 87643 |
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