The ZZ Ceti stars form a class of variable white dwarfs: the hydrogen dominated atmosphere ones, which do pulsate in an instability strip in the effective temperature range 13000K-11500K. We know 22 such ZZ Ceti white dwarfs. Their variations are caused by nonradial g-mode pulsations with periods are in the range 100-1000 seconds. A subsample of

Observational evidence accumulated over the last decade strongly supports the idea that the ionizing radiation field in active galactic nuclei (AGNs) is anisotropic. Here we report on new evidence for this anisotropy in the particular case of the Seyfert 2 galaxy NGC 5252. H I observations of this galaxy reveal neutral gas surrounding the nucleus

It has been known since the work by Claverie et al. (1982) that integrated-sunlight velocities measured with the resonance scattering technique show variations with time scales of weeks to months. The cause can be understood in terms of the effects of solar activity as was pointed out by Edmunds & Gough (1983) and Andersen & Maltby (1983). The

We have analyzed long-slit spectroscopic data for a sample of tidally disturbed elliptical galaxies. Rotation curves and velocity dispersion profiles have been measured at a variety of position angles in these galaxies and have been used to analyze the dynamical response and internal kinematics of stellar systems involved in strong gravitational

During the first few nights following its discovery, we observed the interstellar Ca II and Na I lines towards supernova 1993J at high spectral resolution (full width half maximum (FWHM) approximately 5-6 km/s) with the William Herschel Telescope at La Palma. We find a crowd of absorption components in the radial-velocity range -135 km/s less than

The rapidly variable Seyfert 1 galaxy NGC 4151 will be the subject of an intensive monitoring campaign with IUE, Rosat, GRO, ASCA and ground-based telescopes in December 1993. We will report preliminary results of 9.3 days of continuous monitoring with IUE, at a sampling rate of once every ~ 80 min, an order of magnitude faster than that achieved