THE EVOLVED B[E] STAR HD-87643 - OBSERVATIONS AND A RADIATION-DRIVEN DISC WIND MODEL FOR B[E] STARS

New high-resolution spectroscopic and medium-resolution spectropolarim etric data of the B[e] star HD 87643 are presented, complemented with optical broad- and narrow-band imaging. The spectrum of HD 87643 exhib its the hybrid characteristics well known to be representative of the group of B[e] 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 li nes. Clues to the geometry of the rapidly expanding circumstellar shel l are provided by the startling polarization changes across H alpha. C omparison with published schematic calculations indicates that the pol arizing material is located in a slowly rotating, expanding disc struc ture. A hydrodynamical model is then presented, the results of which a re consistent with the original two-wind concept for B[e] stars, and w hich 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 a nd a slowly expanding disc wind. The model also predicts that the stel lar wind at intermediate latitudes is slower and denser than in the po lar region.