1995A&AS..112..457G

The results of photoelectric UBV observations of the T Tauri type variable BM And made during 1983-1991, as well as of simultaneous photopolarimetric UBVRI observations of this star for 1990-93 are given. In the course of these observations both the brightest (V=11.6)mag and the weakest (V=14.1)mag states of this star were registered. It is shown that the initial reddening of the star during a minimum is stopped at the same brightness level and the star can be bluer in the color U-B during the deepest part of minimum. The decrease of brightness of BM And is accompanied by an increase of linear polarization (up to 3-7%) simultaneously in all UBVRI bands. These changes agree with those observed by Kardopolov & 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 scattered by dust particles in the circumstellar disk is the source of the intrinsic polarization and reduced blue radiation observed at the deepest minima. This intrinsic component of the linear polarization was separated from the observed one. Study of the interstellar (IS) polarization of the nearby stars shows that the IS magnetic field in this region has a regular structure, and the vector of intrinsic linear polarization of BM And is parallel to the lines of magnetic force. The latter means that the circumstellar disk of BM And lies in the plane normal to the IS magnetic field if the disk is optically thin. Such an orientation 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.