2013A&A...549A..79S

Core-collapse supernovae (CC SNe), especially those of type II-plateau (II-P), are thought to be important contributors to cosmic dust production. The most obvious indicator of newly-formed and/or pre-existing dust is the time-dependent mid-infrared (MIR) excess coming from the environment of SNe. In the past few years several CC SNe were monitored by the Spitzer Space Telescope in the nebular phase, hundreds of days after explosion. On the other hand, only a few of these objects have been analyzed and published to date. Our goal was to collect publicly available, previously unpublished measurements on type II-P (or peculiar IIP) SNe from the Spitzer database. The most important aspect was to find SNe observed with the Infrared Array Camera (IRAC) on at least two epochs. The temporal changes of the observed fluxes may be indicative of the underlying supernova, while spectral energy distribution (SED) fitting to the fluxes in different IRAC channels may reveal the physical parameters of the mid-IR radiation, which is presumably caused by warm dust. The IRS spectra were extracted and calibrated with SPICE, while photometric SEDs were assembled using IRAF and MOPEX. Calculated SEDs from observed fluxes were fit with simple dust models to obtain basic information on the dust presumed as the source of MIR radiation. We found twelve SNe that satisfied the criterion above, observed at late-time epochs (typically after +300 days). In three cases we could not identify any point source at the SN position on late-time IRAC images. We found two SNe, 2005ad and 2005af, which likely have newly formed dust in their environment, while in the other seven cases the observed MIR flux may originate from pre-existing circumstellar or interstellar dust. Our results support the previous observational conclusions that warm new dust in the environment of SNe contributes only marginally to the cosmic dust content.