Magnetic field of young star RW Aur
Abstract
Results of longitudinal magnetic field Bz measurements for young star RW Aur A are presented. We found that Bz in the formation region of HeI 5876 line's narrow component varies from -1.47 0.15 kG to +1.10 0.15 kG. Our data are consistent with a stellar rotational period of 5.6d and with a model of two hotspots with an opposite polarity of magnetic field and with a difference in a longitude about 180o. The spot with Bz<0 is located at the hemisphere above the midplane of RW Aur's accretion disc and the spot with Bz>0 is below the midplane. The following upper limits for Bz (at 3σ level) were found after averaging of all our observations: 180 G for photosperic lines, 220 G and 230 G for formation regions of Hα and [OI] 6300 lines respectively. Upper limit 600 G were found in the region where broad components of emisson lines form. For two cases out of 11 we observed the field in a formation region of a blue absorption wing of NaI D lines i.e. in an outflow: Bz= -180 50 G and -810 80 G. Radial velocity of RW Aur's photospheric lines averaged over all our observations is about + 10.5 km/s what is 5.5 km/s less than value derived ten years earlier by Petrov et al. (2001). In this connection, we discuss a possibility that RW Aur is not a binary but a triple system.