DUST AROUND YOUNG STARS - PHOTOPOLARIMETRIC OBSERVATIONS OF THE T-TAURI STAR BM-AND

The results of photoelectric UBV observations of the T Tauri type vari able BM And made during 1983-1991, as well as of simultaneous photopol arimetric UBVRI observations of this star for 1990-93 are given. In th e course of these observations both the brightest (V = 11.m6) and the weakest (V = 14.m1) states of this star were registered. It is shown t hat the initial reddening of the star during a minimum is stopped at t he same brightness level and the star can be bluer in the color U-B du ring the deepest part of minimum. The decrease of brightness of BM And is accompanied by an increase of linear polarization (up to 3-7%) sim ultaneously in all UBVRI bands. These changes agree with those observe d by Kardopolov and Rspaev (1990) and are, in their nature, similar to those observed in Herbig Ae stars with non-periodic Algol-type minima . The similar behavior both of the color index and of the polarization of BM And and of these stars indicates that the stellar radiation sca ttered by dust particles in the circumstellar disk is the source of th e intrinsic polarization and reduced blue radiation observed at the de epest minima. This intrinsic component of the linear polarization was separated from the observed one. Study of the interstellar (IS) polari zation of the nearby stars shows that the IS magnetic field in this re gion has a regular structure, and the vector of intrinsic linear polar ization of BM And is parallel to the lines of magnetic force. The latt er means that the circumstellar disk of BM And Lies in the plane norma l to the IS magnetic field if the disk is optically thin. Such an orie ntation points to the important role of the magnetic field during the initial stage of gravitational collapse of the protostellar cloud from which BM And was formed.