THE HOT-SPOT IN DR TAURI

This paper presents BVRIJHKL light curves for DR Tauri, a pre-main seq uence star in the Taurus-Auriga molecular cloud. We find phased optica l and near-infrared brightness variations with time scales of roughly 5 or 10 days. The lack of a significant time lag indicates that the sa me phenomenon produces these changes. The observed color and flux chan ges suggest a two component model for the excess emission: a bright sp ot with T approximately 10(4) K and a cool region with T approximately 1700 K. We develop a magnetic accretion model to explain the broadban d 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 flo w into the bright spot, which we approximate as a naffow ring symmetri c about the magnetic pole. Radiation from the inner edge of the disk p roduces the flat near-infrared excess in DR Tau; ring emission is resp onsible for the large optical veiling. Our results suggest that an acc retion rate of M approximately 4 X 10(-7) M. yr-1 provides a reasonabl e fit to the spectral energy distribution if the underlying MO star ha s a radius of 2R.. This model can also account for broadband light var iations observed in T Tauri stars if the magnetic axis is inclined rel ative to the stellar rotational axis. Our analysis suggests the sum of the observer's inclination to the rotational axis, i, and the angle b etween the magnetic and the rotational axes, beta, is i + beta approxi mately 95-degrees.