Supernova 1994aj: a probe for pre-supernova evolution and mass-loss from the progenitor

Extensive photometric and spectroscopic observations of SN 1994aj until 540 d after maximum light have been obtained. The photometry around maximum suggests that the SN belongs to the Type TI Linear class, with a peak absolute magnitude of M(V) similar to -17.8 (assuming H(0)=75 km s(-1) Mpc(-1)). The spectra of SN 1994aj unusual, with the presence of a narrow line with a P Cygni profile on top of the broad Balmer line emission. This narrow feature is attributed to the presence of a dense superwind surrounding the SN. At 100-120 d after maximum light the SN ejecta start to interact with this circumstellar material, The SN luminosity decline rates slowed down [gamma(R)=0.46 mag (100 d)(-1)], becoming less steep than the average late luminosity decline of normal SN II [similar to 1 mag (100 d)(-1)]. This dense ((M) over dot /u(W) similar to 10(15) g cm(-1)) wind was confined to a short distance from the progenitor (R(out)=similar to 5 x 10(16) cm), and results from a very strong mass-loss episode ((M) over dot=10(-3) M. yr(-1)), which terminated shortly before explosion (similar to 5-10 yr).