The results of optical spectroscopy and photometry of V404Cyg, the optical counterpart of the recently discovered X-ray transient GS2023 + 338, are presented. Optical spectra were obtained at the Roque de los Muchachos Observatory with the 2.5-mm Isaac Newton Telescope. The overall optical light curve was found to be similar to that of an earlier

SE COMIENZA CON UNA DESCRIPCION DE LOS PROBLEMAS MAS IMPORTANTES QUE APARECEN EN EL ESTUDIO DE LAS POBLACIONES ESTELARES, ASI COMO DE LOS METODOS EMPLEADOS HASTA AHORA PARA SU TRATAMIENTO. A PARTIR DE ESTA INTRODUCCION SE MUESTRAN LOS MODELOS DESARROLLADOS EN ESTE TRABAJO, DETALLANDO TANTO LOS METODOS MATEMATICOS COMO LAS IDEAS FISICAS SOBRE LAS

Simultaneous UBVRI photopolarimetric observations of the highly variable BL Lac object OJ 287 have been obtained on six nights. The polarization and position angle, as well as their wavelength dependence, have been found to be variable from night to night and also on a timescale of a few hours. During the first three consecutive nights, a clear

Redshift observations of 30 clusters in the direction of the Sextans-Leo supercluster candidate are reported. The observations are part of a program which involves mapping the universe's large-scale structure, and include North Galactic Cap Abell clusters, Abell clusters that have only been partially observed, and unmeasured poor Zwicky clusters

The site of the solar spectrometer of the International Research on the Interior of the Sun (IRIS) network, installed in December 1989 in the Teide Observatory (Izana, Tenerife) is described together with the instrumental facilities of the Teide Observatory. The IRIS instrument is housed at the Solar Oscillation Laboratory of the observatory, which

The present study of the local insterstellar medium toward the center of Loop I analyzes optical and UV spectra of nearby stars within the l = 310-330 deg, b = 15-25 deg area. The analysis of the UV spectra reveals a sudden gas-column density increase as a function of distance from 10 to the 18th to 10 to the 20th/sq cm, suggesting the presence of