In this contribution we discuss new results of a program aimed at studying the physical properties, origin and evolution of ``low-ionization, small-scale structures in PNe''. Within this project we classify and discuss the properties of a sample of more than 50 PNe, collected from the literature, in the light of their possible formation mechanisms

We describe a new LTE inversion code for the analysis of Stokes profiles emerging from unresolved magnetic elements. It has been specifically designed to obtain the thermal, dynamic, and magnetic properties of these structures in a self-consistent manner by fitting the whole shape of the observed spectra. The inversion code is based on a previous

Let $X$ be a compact Kahler manifold, and let $L$ be a line bundle on $X.$ Define $I_k(L)$ to be the kernel of the multiplication map $ Sym^k H^0 (L) o H^0 (L^k).$ For all $h leq k,$ we define a map $ ho : I_k(L) o Hom (H^{p,q} (L^{-h}), H^{p+1,q-1} (L^{k-h})).$ When $L = K_X$ is the canonical bundle, the map $ ho$ computes a second fundamental

SAO 85766 (b = +20o) is an IRAS source with far-infrared colours similar to planetary nebulae. According to the HDE catalogue, its spectrum in 1940 was that of an A5 star. The UV fluxes and colours derived from data obtained by the TD1 satellite in 1972 also indicate that SAO 85766 was an A-type supergiant at that epoch. However, high resolution

We study the effect of microturbulence in the line formation calculations of H and He lines, in the parameter range typical for O and early B stars. We are specially interested in its effect on the determination of stellar parameters: Teff, log g and specially on the He abundance. We first analyze the behaviour of H and He model lines between 4 000

We present a mechanism to produce X-ray transient periodic variations in AGN. This mechanism is triggered off by Compton scattering in the infalling plasma into a black hole, which can induce an electric charge in the singularity. The charging and discharging processes can affect the X-ray luminosity of AGN.