We present a 0.8–2.5 μm spectrum of the peculiar variable V838 Mon, obtained on 2002 October 29. We see one of the coolest stars – certainly the coolest supergiant – ever observed, with deep water bands and other spectral signatures normally associated with very late L and T brown dwarfs. We suggest that V838 Mon may be the first known ‘L supergiant’.

Nova Cassiopeiae 1993 (V705 Cas) was an archetypical dust-forming nova. It displayed a deep minimum in the visual light curve, and spectroscopic evidence for carbon, hydrocarbon and silicate dust. We report the results of fitting the infrared (IR) spectral energy distribution (SED) with the DUSTY code, which we use to determine the properties and geometry of the emitting dust. The emission is well described as originating in a thin shell whose dust has a carbon:silicate ratio of 2:1 by number (∼1.26:1 by mass) and a relatively flat size distribution. The 9.7-and 18-µm silicate features are consistent with freshly condensed dust and, while the lower limit to the grain size distribution is not well constrained, the largest grains have dimensions ∼0.06 µm; unless the grains in V705 Cas were anomalously small, the sizes of grains produced in nova eruptions may previously have been overestimated in novae with optically thick dust shells. Laboratory work by Grishko & Duley may provide clues to the apparently unique nature of nova unidentified infrared (UIR) features.

Abstract. We present the results of our analysis of a high resolution (R 30 000) infrared spectrum of V4334 Sgr (Sakurai's Object) around the first overtone CO bands, obtained in 1998 July. The 12 CO and 13 CO bands are well-resolved, and we compute synthetic hydrogen-deficient model atmosphere spectra to determine the 12 C/ 13 C ratio. We find 12 C/ 13 C 4 ± 1, consistent with the interpretation of V4334 Sgr as an object that has undergone a very late thermal pulse.

We present an observation of the very late thermal pulse object V4334 Sgr (Sakurai's Object) with the Infrared Spectrometer (IRS) on the Spitzer Space Telescope. The emission from 5–38 μm is dominated by the still‐cooling dust shell. A number of features are seen in absorption against the dust shell, which we attribute to HCN and polyyne molecules. We use these features to determine the 12C/13C ratio for the absorbing gas to be ∼3.2+3.2−1.6; this implies that, despite the H‐content of the molecules, the hydrocarbon‐bearing gas must have originated in material produced in the very late thermal pulse. We see no evidence of emission lines, despite the recently‐reported optical and radio observations that suggest the effective temperature of the stellar remnant is rising.

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