  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 the presence of newly-formed and/or pre-existing dust
is the time-dependent mid-infrared (MIR) excess coming from the environment of
SNe. Our goal was to collect publicly available, previously unpublished
measurements on type II-P (or peculiar IIP) SNe from the Spitzer database. 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, presumably due to warm dust. 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
get basic information on the dust presumed as the source of MIR radiation. We
found twelve SNe satisfying 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 cosmic dust content.
