Optical and radio observations of the BL Lacertae object OJ 287 made early in 1989 show a sudden fade in both wavelength ranges. From January to early April the V magnitude was near 16. However, in late April and early May B = 18.4, V = 17.4, R = 16.7 and I = 15.8 were observed. At the same time, the flux at 22 GHz and 37 GHz fell to 1.9 Jy and 1.7

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