Photometric and spectroscopic evolution of the Type IIP supernova SN 2004et

We present optical photometry and spectroscopy of the Type IIP supernova SN 2004et that occurred in the nearby galaxy NGC 6946. The observations span a time range of 8-541 d after explosion. The late time bolometric luminosity and the Ha luminosity in the nebular phase indicate that 0.06 +/- 0.02 M-circle dot of Ni-56 was synthesized during the explosion. The plateau luminosity, its duration and the expansion velocity of the supernova at the middle of the plateau indicate an explosion energy of E-exp = 1.20(-0.30)(+0.38) x 10(51) erg. The late time light curve and the evolution of the [O I] and H alpha emission-line profiles indicate the possibility of an early dust formation in the supernova ejecta. The luminosity of [O I] 6300, 6364 angstrom doublet, before the dust formation phase, is found to be comparable to that of SN 1987A at similar epochs, implying an oxygen mass in the range 1.5-2M(circle dot), and a main-sequence mass of 20M(circle dot) for the progenitor.