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 II Linear class, with a peak absolute magnitude of MV∼−17.8 (assuming H0=75 km s−1 Mpc−1). The spectra of SN 1994aj were 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 [γR=0.46 mag (100 d)−1], becoming less steep than the average late luminosity decline of normal SN II [∼1 mag (100 d)−1]. This dense (˙M/uW∼1015 g cm−1) wind was confined to a short distance from the progenitor (Rout=∼5×1016 cm), and results from a very strong mass-loss episode (˙M=10−3 M⊙ yr−1), which terminated shortly before explosion (∼5–10 yr).