The variability of the broad emission lines in Seyfert galaxies is naturally explained in terms of photo-ionization models of the broad line region (BLR) as the response of the emitting gas to changes in the central ionizing continuum. An analysis is made of the response to a single continuum event of a simple model of the BLR consisting of an

New long-slit optical spectroscopy and optical and NIR images of NGC 520 are presented. Velocity-dispersion and radial-velocity profiles are obtained from the spectra with the Fourier quotient and cross-correlation techniques. At the NW optical emission peak, a sharp rise in the velocity dispersions implies a concentration of mass. The NW optical

Observations of interstellar absorptions superposed on the chromospheric Mg II emissions of nearby cool stars have been used to explore the structure of the local interstellar medium along many lines of sight. The interstellar cloud in which the sun is immersed (the 'local cloud', hereafter LC) has not previously been detected using this technique

The photometric distortion waves in the light curves of the short-period RS CVn system BH Vir by a dark, circular spot model for the active regions on the primary star is parameterized. Recent observations and archival sources are used to infer the positions and areas of the active regions. For light curves with simultaneous B and R or V and I data

From H-alpha CCD observations taken with the 4.2-m William Herschel Telescope, a catalog of 456 H II regions of the inner zone of the spiral galaxy NGC 4321 has been compiled. The radial distribution, the distribution of diameters, and the luminosity function for the arm and the interarm H II regions are presented, together with the spatial

Results are presented on an analysis of rapid photometric data of the F2 V star HD 155543, obtained simultaneously from the Observatorio del Teide (Spain) and the Observatorio de San Pedro Martir (Mexico) during May-June, 1987. Strong evidence was found of the presence in this star of acoustic p-mode spectrum; when performing a squared amplitude of