  We have analyzed all the observations of BP Tauri taken by the International
Ultraviolet Explorer in the low resolution (6 A), long wavelength (from 1850 to
  3350 A) range. This dataset contains 61 spectra. These spectra do not show
any correlation between the continuum flux and the MgII line flux, thus
resolving a standing controversy in the literature concerning the origin of the
MgII 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 developed by Calvet & Gullbring (1998), we obtain energy fluxes,
accretion spot sizes, and accretion rates from the IUE observations of BP
Tauri. We find average energy fluxes of 5.0 10^11 ergs cm^{-2} s^{-1}, average
spot sizes of 4.4 10^{-3} times the stellar surface, and average accretion
rates of 1.6 10^-8 msun/yr. Our analysis shows that the particle energy flux
and the UV flux in the stellar surface are proportional to each other. Most
strikingly, we observe a correlation between accretion rate and spot size, with
the spot size increasing as the square of the accretion rate. Based on the
results of a simulation, we conclude that geometrical effects are not enough to
account for this effect. Current models of the accretion process fail to
reproduce such an effect, suggesting the need of using more realistic
descriptions of the stellar field when treating magnetospheric accretion. There
may also be an unmodelled efficiency factor that determines how matter is
loaded into the field lines.
