2011MNRAS.418.1285F

We present an analysis of multi-epoch observations of the Type II-P supernova SN 2004et. New and archival optical spectra of SN 2004et are used to study the evolution of the Hα and [O I] 6300-Å line profiles between days 259 and 646. Mid-infrared imaging with Michelle on Gemini-North and with all three instruments of the Spitzer Space Telescope was carried out between 2004 and 2010, supplemented by archival Spitzer data. We include Spitzer`warm' mission photometry at 3.6 and 4.5 µm obtained on days 1779, 1931 and 2151, along with ground-based and Hubble Space Telescope (HST) optical and near-infrared observations obtained between days 79 and 1803. Multiwavelength light curves are presented, as well as optical–infrared spectral energy distributions (SEDs) for multiple epochs. Starting from about day 300, the optical light curves provide evidence for an increasing amount of circumstellar extinction attributable to newly formed dust, with the additional extinction reaching 0.8–1.5 mag in the V band by day 690. The overall SEDs were fitted with multiple blackbody components, in order to investigate the luminosity evolution of the supernova, and then with Monte Carlo radiative transfer models using smooth or clumpy dust distributions, in order to estimate how much new dust condensed in the ejecta. The luminosity evolution was consistent with the decay of ⁵⁶Co in the ejecta up until about day 690, after which an additional emission source is required, in agreement with the findings of Kotak et al. Clumped dust density distributions consisting of 20 per cent amorphous carbons and 80 per cent silicates by mass were able to match the observed optical and infrared SEDs, with dust masses that increased from 8 {x} 10^–5 M_☉ on day 300 to 1.5 {x} 10^–3 M_☉ on day 690, still significantly lower than the values needed for core-collapse supernovae to make a significant contribution to the dust enrichment of galaxies.