(Hα+[NII])/[OIII] ratio images have been used to search for low-ionization small-scale structures in a sample of 258 planetary nebulae. Radially symmetrical knots or jet-like structures, which are enhanced in the ratio images compared to the neighbouring regions of the nebulae, have been identified in 23 objects. Some of these features are barely

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We present three-dimensional numerical calculations of superbubbles evolving in a two-component interstellar medium composed of small diffuse clouds and a low-density intercloud medium. Cold H I clouds with internal densities n ˜ 10 cm-3 and radii Rcl = 3-5 pc were assumed to be embedded in a warm plane-stratified intercloud medium. The fraction of

We obtain the NaI lambdalambda8183, 8195 absorption-line radial velocity curves for the polars ST LMi and MR Ser, from which we find the semi-amplitudes to be K_abs=329+/-6 and 289+/-9 km s^-1 respectively. We find that for both systems the effects on the NaI absorption lines due to X-rays heating the inner face of the secondary are negligible, and

High and low resolution spectroscopy, together with narrow and broad band imaging have been acquired for the unusual outflow source NGC 7026. We find evidence for appreciable changes in excitation, and a highly variable emission structure, consistent in part with observed variations in electron density. The mean electron density is found to be n_e_

We have calibrated the effective temperatures of the low main sequence stars ranging spectral types from F0 to K5 versus [Fe/H] and colours (B-V), (R-I), (V-R), (V-I), (V-K), (J-H), (J-K) and ubvy-β, using a large sample of dwarfs and subdwarfs. The effective temperatures, scaled to direct T_eff_ determinations via reliable angular diameter