Photopolarimetric activity and circumstellar environment of the young binary system DF Tau

¹ Crimean Astrophysical Observatory, Crimea, 334413 Nauchny, Ukraine e-mail: grinin@crao.crimea.ua
² Pulkovo Astronomical Observatory, St. Petersburg 198904, Russia e-mail: grinin@vg1723.spb.edu
³ Max-Plank Institute fur Radioastronomie, Bonn, Germany e-mail: weigelt@mpifr-bonn.mpg.de
⁴ Special Astronomical Observatory, Russia
⁵ Astronomical Institute, Tashkent, Uzbekistan

Received: 28 July 2005
Accepted: 27 October 2005

Abstract

We present the results of multi-year photometric and polarimetric observations of the young binary system DF Tau in the UBVRI bands, as well as bispectrum speckle interferometric observations in the H and K bands obtained between 2001 and 2003. The photometric and polarimetric observations suggest that the linear polarization of DF Tau does not depend on its brightness, and the polarization variation has a stochastic character. This result confirms earlier suggestions about the dominant role of hot accretion spots in the photometric activity of this star. We argue that the hot spots are at high latitudes and/or the star rotation axis is inclined to the line-of-sight. The influence of circumstellar (CS) dust on the variability is probably small since the inclination of the primary's CS disk to the line-of-sight is large.
Using the total mass of the binary system DF Tau from Hartigan & Kenyon (2003, ApJ, 583, 334), we calculated new orbital parameters of the system. The new value of the orbital period ( yr) disagrees with the photometric cycle of about 40 yr revealed by Lamzin et al. (2001b, A&A, 372, 922) from analysis of the historical light curve of this star. This suggests that this cycle is not caused by the orbital motions of the binary components, but probably reflects the cyclical variability of the global magnetic field on the main component.