UV spectra of T Tauri stars from the HST and IUE satellites: BP Tau

Ultraviolet spectra of BP Tau observed with HST/GHRS and IUE satellites wer e analysed. We found that BP Tau activity can be explained in the frame of a disk accretion model if we assume that the stellar magnetic axis is stron gly inclined to the disk plane. The following set of accretion process para meters were derived: relative surface area of the accretion zone f similar or equal to 0.25; accretion rate M-ac similar to 3.6 x 10(-8) M-circle dot yr(-1), accretion energy flux F = 2.3 x 10(10) erg s(-1) cm(-2) and accreti on luminosity L-ac similar or equal to 0.37 L-circle dot. The relevance of these parameters is discussed. We argue that the Calvet & Gullbring (1998) accretion shock model is too crude to believe that the accretion spot surfa ce area is indeed proportional to the square of the accretion rate, as Ardi la & Basri (2000) found through this model. A strong are in the Fe II 2811. 8, 2812.1 Angstrom lines was detected, it was probably produced by an incre ase of the accretion rate. During the are, the accretion luminosity was com parable to or even larger than the stellar bolometric luminosity.