1999A&A...341..553P

The T Tauri star RY Tau has increased its brightness from V=10.6mag to V=9.6mag in October-November 1996. By February-March 1997, the star has faded again to V=10.8mag. High-resolution echelle spectra of RY Tau were obtained with the SOFIN spectrograph at the Nordic Optical Telescope (La Palma, Spain) at low and high brightness levels of the star. No significant changes in the photospheric lines, which are sensitive to temperature and gravity, were noticed. The spectral type of RY Tau is defined as G1-2IV, which in combination with photometric data implies A_V=1.0-1.3mag. Polarimetric patrol of RY Tau during the fading of the star showed an increase of its intrinsic polarization from 0.5-1.0% at high brightness to about 2% at low brightness in the V, R and I bands. The flux radiated in Hα and the IR Ca II emission lines remained about the same, in spite of the one magnitude difference in the continuum flux. These results indicate that variable obscuration of the star by circumstellar dust clouds was responsible for the brightness change of RY Tau, and that the emission line source is mostly outside of the obscured region.