SIMBAD references

We present simultaneous multicolour photometric and polarimetric observations of the T Tauri stars RY Tau, V1121 Oph, DI Cep and BM And. Significant variabilities on time-scales of days in the degree of polarization and/or in the position angle were recorded for DI Cep and BM And. None of the stars reveiled changes in the polarization properties on time-scales shorter than one day. One star, BM And, showed anti-correlations between its brightness level and degree of polarization, consistent with a period of ∼4days. The change of its position angle of ∼25deg implies the presence of a strongly variable intrinsic polarization relative to a constant interstellar polarization component. We speculate that it is caused by irradiation of a hot spot. The presence of a hot source is also indicated by the photometric measurements. DI Cep increased its brightness by 0.5magnitudes during four nights while its degree of polarization and the position angle showed only modest variations. V1121 Oph showed a wavelength dependent rotation of its polarization vector with an increase in the position angle of ∼43deg from the U band to the I band.