The Type IIP SN 2007od in UGC 12846: from a bright maximum to dust formation in the nebular phase*

Ultraviolet, optical and near-infrared observations of the Type IIP supernova (SN) 2007od, covering from maximum light to late phases, allow detailed investigation of different physical phenomena in the expanding ejecta. These data turn this object into one of the most peculiar SNe IIP ever studied. The early light curve of SN 2007od is similar to that of a bright IIP, with a short plateau, a bright peak (M V = -18 mag), but a very faint late-time optical light curve. However, with the inclusion of mid-IR observations during the radioactive tail, we derive an ejected mass of 56 Ni of M( 56 Ni) 2 10 -2 M . By modelling the bolometric light curve, ejecta expansion velocities and blackbody temperature, we estimate a total ejected mass of 5-7.5 M with a kinetic energy of at least 0.5 10 51 erg. The early spectra reveal a boxy H profile and high-velocity features of the Balmer series that suggest the possible interaction of the ejecta with a close circumstellar matter (CSM). The interaction with the CSM and the presence of dust formed inside the ejecta are evident in the late-time spectra. The episodes of mass-loss shortly before explosion, the bright plateau, the relatively small amount of 56 Ni and the faint [O I] emission observed in the nebular spectra are consistent with a super-asymptotic giant branch progenitor (M 9.7-11 M ).