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

Extensive photometric and spectroscopic observations of SN1994aj until 540d after maximum light have been obtained. The photometry around maximum suggests that the SN belongs to the Type II Linear class, with a peak absolute magnitude of M_V~-17.8 (assuming H_0=75 km s^-1 Mpc^-1). The spectra of SN1994aj were unusual, with the presence of a narrow line with a PCygni 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 100-120d 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 (100d)^-1], becoming less steep than the average late luminosity decline of normal SNII [~1 mag (100d)^-1]. This dense (_solarM/u_W~10^15 g cm^-1) wind was confined to a short distance from the progenitor (R_out=~5x10^16 cm), and results from a very strong mass-loss episode (_solarM=10^-3 Msolar yr^-1), which terminated shortly before explosion (~5-10 yr).