Optical observations of type-IIP supernova 2004dj:: Evidence for asymmetry of the 56Ni ejecta

Photometric and spectroscopic observations of the nearby type-IIP supernova 2004dj are presented. The Ni-56 mass in the envelope of SN 2004dj was estimated from the light curve to be approximate to 0.02M(circle dot). This estimate is confirmed by modeling the Ha luminosity. The Ha emission line exhibits a strong asymmetry characterized by the presence of a blue component in the line with a shift of -1600 km s(-1) at the early nebular phase. A similar asymmetry was found in the H beta, [O I], and [Ca II] lines. The line asymmetry is interpreted as being the result of asymmetric Ni-56 ejecta. The Hoe profile and its evolution are reproduced in the model of an asymmetric bipolar Ni-56 structure for a spherical hydrogen distribution. The mass of the front Ni-56 jet is comparable to that of the central component and twice that of the rear Ni-56 jet. We point out that the asymmetric bipolar structure of 16 Ni ejecta is also present in SN 1999em, a normal type-IIP supernova. (c) 2005 Pleiades Publishing, Inc.