We present detailed analysis of mid-infrared (MIR) data for 9 type II-P supernovae from the public Spitzer database. Spectral energy distributions (SEDs) from observed fluxes are fitted with simple models to get basic information about the dust as the presumed source of MIR radiation. 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.

I have examined all InfraRed Astronomy Satellite (IRAS) data relevant to the 173 galactic Wolf-Rayet (WR) stars in an updated catalogue provided by van der Hucht (priv. comm.), including the 13 stars newly discovered by Shara et al. (1991). Using the exact coordinates given in these lists, I have examined the IRAS Point Source Catalog (PSC), the Faint Source Catalog, Faint Source Reject Catalog, and generated 1-dimensional spatial profiles (“ADDSCAN”s), and 2-dimensional full-resolution images (“FRESCO”s). The goal was to assemble the best set of observed IRAS colour indices for different WR types, in particular for known dusty WCL objects. These colour indices define zones in the IRAS colour-colour plane. By searching the PSC for otherwise unassociated sources that satisfy these colours, I have identified potential new WR candidates, too faint to have been recognized in previous optical searches. I have extracted these candidates' IRAS Low Resolution Spectrometer (LRS) data and compared the spectra with the highly characteristic LRS shape for known dusty WCL stars. Any surviving candidates must now be examined by optical spectroscopy. This work represents a much more rigorous and exhaustive version of the LRS study that identified IRAS 17380-3031 (WR98a) as the first new WR (WC9) star discovered by IRAS (Cohen et al. 1991).

WC-type Wolf-Rayet stars show episodic or persistent infrared emission attributed to amorphous carbon grains forming in their winds. The process of dust formation in the hydrogen-poor environments characteristic of WC winds is reviewed and compared to the chemical pathway to soot particle production in AGB stars. Emphasis is put on the formation of the dust precursors, and the physical conditions necessary to nucleate them in WC winds. In particular, it is concluded that dust formation around WC stars occurs in a dense, largely neutral, circumstellar disk.

At first sight, it is surprising that dust nucleation and growth can occur in the harsh environment of a Wolf-Rayet star wind. However, we know that episodic formation occurs in several different types of astrophysical source. Of particular relevance to our efforts to gain a fuller understanding of the process in WC stars is the extensive work that has been performed on classical novae. Thus, although episodic dust formation in other types of object is briefly described, this review concentrates on a comparison with this process as observed in novae in particular. It is argued that for efficient grain growth, clumping of ejecta (perhaps following shock-interactions) is essential.

The physical properties of dust in WR shells are investigated in detail. It has been found that carbon grains may grow in the severe conditions of WR shells due to collisions with impinging positive carbon ions. Detailed physical models of carbon dust and dust production rates for selected WC stars have been calculated. It is concluded that graphite rather than amorphous carbon is the most suitable grain material.