This is a study of the UV variability of the galaxy Fairall-9 between 1978 and 1991. Table 1 shows the UV continuum fluxes measured in three "line-free" windows centered at 1171, 1400 and 1910 A (observed wavelengths), and corrected for E(B-V)=0.035 extinction. The IUE Fine Error Sensor (FES) counts (optical photometry) are also given in this table

We present long-slit spectra of the Seyfert 2 galaxy NGC 5252, covering the nucleus and part of the extranuclear emission-line region. All the regions sampled by our spectra have emission-line ratios characteristic of photoionization by an active galactic nucleus-like (AGN-like) continuum source. The spectrum of the nucleus differs from those

New spectroscopic observations, including the optical and near-infrared ranges, have been obtained for a sample of HII regions located towards the Galactic anticentre. The sample includes HII regions with known galactocentric distances, their ionizing stars having been clearly identified from previous work. The spectra correspond to low-to

Here we describe a method that can be used to derive, with a high degree of confidence, the direction of the rotation axis of a galaxy. The method is based on the deformation, caused by differential galactic rotation, of the remnants produced by multi-supernova explosions. We consider two realistic extreme sets of galactic boundary conditions, and

Plage areas and intensities derived from CaIIK spectroheliograms are used as a proxy for the facular irradiance excess of solar active regions for the period 19 August to 4 September 1980. Applying a calibration method proposed by Vrsnak et al. (1991) and adopting it for photometrically measured plage intensities, the "Photospheric Facular Index"

LA TESIS PRESENTADA EXPONE UN NUEVO METODO PARA DERIVAR LA HISTORIA DE LA FORMACION ESTELAR EN GALAXIAS IRREGULARES ENANAS. INTENTOS ANTERIORES SE HAN VISTO SIEMPRE MUY LIMITADOS DEBIDOS A LA DIFICULTAD DE SEPARAR LOS EFECTOS DE LA EDAD Y LA METALICIDAD DE LAS ESTRELLAS, JUNTO CON LAS INCERTIDUMBRES EN DIFERENTES PARAMETROS (EL RITMO DE FORMACION