Magnetic field of young star RW Aur

TL;DR

This study measures the magnetic field of young star RW Aur, revealing magnetic polarity variations, potential stellar rotation, and upper limits on magnetic field strength in different regions, suggesting complex magnetic and possibly multiple star system dynamics.

Contribution

First detailed magnetic field measurements of RW Aur's formation regions, proposing a two-spot magnetic model and discussing the star's possible triple system nature.

Findings

Magnetic field varies from -1.47 kG to +1.10 kG in the formation region.

Consistent with a 5.6-day stellar rotation period.

Upper limits of 180-230 G for various regions, with some outflow measurements.

Abstract

Results of longitudinal magnetic field B_z measurements for young star RW Aur A are presented. We found that B_z in the formation region of HeI 5876 line's narrow component varies from -1.47 \pm 0.15 kG to +1.10 \pm 0.15 kG. Our data are consistent with a stellar rotational period of \simeq 5.6^d and with a model of two hotspots with an opposite polarity of magnetic field and with a difference in a longitude about 180^o. The spot with B_z<0 is located at the hemisphere above the midplane of RW Aur's accretion disc and the spot with B_z>0 is below the midplane. The following upper limits for B_z (at 3\sigma{} level) were found after averaging of all our observations: 180 G for photosperic lines, 220 G and 230 G for formation regions of H_\alpha{} 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: B_z= -180 \pm 50 G and -810 \pm 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.