THE HOT-SPOT IN DR TAURI

This paper presents BVRIJHKL light curves for DR Tauri, a pre-main sequence star in the Taurus-Auriga molecular cloud. We find phased optical and near-infrared brightness variations with time scales of roughly 5 or 10 days. The lack of a significant time lag indicates that the same phenomenon produces these changes. The observed color and flux changes suggest a two component model for the excess emission: a bright spot with T approximately 10(4) K and a cool region with T approximately 1700 K. We develop a magnetic accretion model to explain the broadband spectral energy distribution and optical light curves of DR Tau. The magnetic field truncates the inner disk at a distance of five stellar radii from the central MO star. This field channels the accretion flow into the bright spot, which we approximate as a naffow ring symmetric about the magnetic pole. Radiation from the inner edge of the disk produces the flat near-infrared excess in DR Tau; ring emission is responsible for the large optical veiling. Our results suggest that an accretion rate of M approximately 4 X 10(-7) M. yr-1 provides a reasonable fit to the spectral energy distribution if the underlying MO star has a radius of 2R.. This model can also account for broadband light variations observed in T Tauri stars if the magnetic axis is inclined relative to the stellar rotational axis. Our analysis suggests the sum of the observer's inclination to the rotational axis, i, and the angle between the magnetic and the rotational axes, beta, is i + beta approximately 95-degrees.