We present the near infrared photometry of a new sample of 225 IRAS sources, many of them previously unidentified in the literature, selected because their far infrared colours are similar to those shown by known planetary nebulae. The results obtained are used to establish the main source of near infrared emission. Combining this information with

The first results of an observational programme aimed at mapping a sample of face-on spiral galaxies in the NIR are presented. This paper shows the surface photometry of the first ten galaxies in the sample. The data were taken in the broad band J (1.2 mu m) and Ks (2.2 mu m) filters. The sources were selected mainly according to their size and

In this paper we address the problem of the non-LTE (NLTE) inversion of line profiles by means of a nonlinear least-squares minimization procedure combined with very efficient multilevel transfer methods. Our approach is based on the concept of response functions, which measure the first-order response of the emergent profiles to changes in the

First results from a high-resolution three-dimensional nonlinear numerical study of the kink oscillation are presented. We show in detail the development of a shear instability in an untwisted line-tied magnetic flux tube. The instability produces significant deformations of the tube boundary. An extended transition layer may naturally evolve as a

The nonlinear development of the kink instability of a magnetic flux tube initially lying in mechanical equilibrium in the deep convection zone is presented. The unstable evolution is started by a small-amplitude sinusoidal perturbation of the shape of the flux tube in a vertical plane. As a result of the development of the instability, the lower

IAUC 4489 available at Central Bureau for Astronomical Telegrams. IAUC 4489 available at Central Bureau for Astronomical Telegrams.