The Balmer wavelength range of BP Tauri

We have analyzed all the observations of BP Tauri taken by the Internationa l Ultraviolet Explorer (IUE) in the low-resolution (Delta lambda similar to 6 Angstrom), long-wavelength (lambda = 1850-3350 Angstrom) range. This dat a set contains 61 spectra. We observe variability in the ultraviolet contin uum of Delta m(cont) similar to 1 mag and variability in the Mg II line flu x of Delta m(Mg II) similar to 0.8 mag. Moreover, these spectra do not show any correlation between the continuum flux and the Mg II line flux, thus r esolving a standing controversy in the literature concerning the origin of the Mg II line flux. There is no correlation between the color temperature of the UV continuum and the average value of its flux. Using models of the accretion process recently developed by other authors, we obtain energy flu xes, accretion spot sizes, and accretion rates from the IUE observations of BP Tauri. We find average energy fluxes of 5.0 x 10(11) ergs cm(-2) s(-1) average spot sizes of 4.4 x 10(-3) times the stellar surface, and average a ccretion rates of 1.6 x 10(-8) M. yr(-1) Our analysis shows that the partic le energy flux and the UV flux in the stellar surface are proportional to e ach other. Most strikingly, we observe a correlation between accretion rate and spot size, with the spot size increasing as the square of the accretio n rate. Based on the results of a simulation, we conclude that geometrical effects (i.e., the varying inclination of the spot with respect to the obse rver) are not enough to account for this effect. Current models of the accr etion process fail to reproduce such an effect, suggesting the need of usin g more realistic descriptions of the stellar field when treating magnetosph eric accretion. There may also be an unmodeled efficiency factor that deter mines how matter is loaded into the field lines. Nondipole fields, geometry , oblique shocks, and the possibility of "limb brightening" should be taken into account when creating models and explaining the results of observatio ns of T Tauri stars.