We present mid-infrared (2-12 µm) spectra of the microquasar SS 433 obtained with the Infrared Space Observatory (spectroscopic mode of ISOPHOT and ISOCAM). We compare them to the spectra of four Wolf-Rayet stars: WR 78, WR 134, WR 136, and WR 147 in the same wavelength range. The mid-infrared spectrum of SS 433 mainly shows H i and He i emission lines and is very similar to the spectrum of WR 147, a WN8(h)+B0.5V binary. The 2-12 µm continuum emission of SS 433 corresponds to optically thin and partially optically thick free-free emission, from which we calculate a mass loss rate of 2−3 × 10 −4 M yr −1 if the wind is homogeneous and a third of these values if it is clumped. This is consistent with a strong stellar wind from a WN star. However, following recent studies concluding that the mass donor star of SS 433 is not a Wolf-Rayet star, we propose that this strong wind out flows from a geometrically thick envelope of material that surrounds the compact object like a stellar atmosphere, imitating the Wolf-Rayet phenomenon. This wind could also wrap the mass donor star, and at larger distances (∼40 AU), it might form a dust envelope from which the thermal emission, detected with ISOPHOT at 25 µm and 60 µm, would originate. This wind also probably feeds the material that is ejected in the orbital plane of the binary system and that forms the equatorial outflow detected in radio at distances > 100 AU.

We present infrared observations of the supernova remnant G21.5-0.9 with the Very Large Telescope, the Canada-France-Hawaii Telescope and the Spitzer Space Telescope. Using the VLT/ISAAC camera equipped with a narrow-band [Fe II] 1.64 μm filter the entire pulsar wind nebula in SNR G21.5-0.9 was imaged. This led to detection of iron line-emitting material in the shape of a broken ring-like structure following the nebula's edge. The detected emission is limb-brightened. We also detect the compact nebula surrounding PSR J1833-1034, both through imaging with the CFHT/AOB-KIR instrument (K band) and the IRAC camera (all bands) and also through polarimetric observations performed with VLT/ISAAC (K s band). The emission from the compact nebula is highly polarised with an average value of the linear polarisation fraction P avg L 0.47, and the swing of the electric vector across the nebula can be observed. The infrared spectrum of the compact nebula can be described as a power law of index α IR = 0.7 ± 0.3, and suggests that the spectrum flattens between the infrared and X-ray bands.

Abstract. We present broadband optical polarimetry of the classical novae V705 Cas, V4362 Sgr, V2313 Oph and BY Cir in outburst. The data indicate that, in all cases, there is an intrinsic component of polarization and in some cases the variability is very rapid, on a time-scale ∼1 day. In the case of V705 Cas, we suggest that the origin of the intrinsic component may lie in the clumpiness and/or inhomogeneities of the ejecta, while electron scattering is the most likely cause in V2313 Oph. The wavelength-dependence of polarization in the case of V4362 Sgr suggests scattering by small dust grains, while polarization in resonance lines is the most probable cause of the observed polarization in BY Cir.