We present a study of the atmospheric extinction over the observatories of the Canary Islands, based mainly on photometric measurements of the V-band extinction coefficient obtained during /2850 nights at the Carlsberg Automatic Meridian Circle at the Roque de los Muchachos Observatory (La Palma), and complemented with visible and infrared data

The knowledge of accurate distances to Planetary Nebulae (PNe) is necesary in order to improve the determination of some physical quantities such as the nebular radius and mass. The nebular mass is a critical parameter to determine the amount of mass that is returned to the interstellar medium by the PN. This mass return can influence the evolution

A substellar-mass object in orbit at about 300 astronomical units (AU) from the young low-mass star G196-3 was detected by direct imaging. Optical and infrared photometry and low- and intermediate-resolution spectroscopy of the faint companion, hereafter referred to as G196-3B, confirms its cool atmosphere and allows its mass to be estimated at 25^

Atmospheric extinction data covering a long period are analysed. We present infrared atmospheric extinction in the J, H and K bands obtained at the Teide Observatory from 1989 to 1997. We find high-quality statistical values, similar to those of other good sites, such as Mauna Kea. We devote special attention to the study of the dependence of the

A search for bright galaxies associated with radio sources from the WENSS minisurvey has been carried out. A galaxy counterpart was found for 402 of almost 10,000 radio sources. Of these a radio and optically complete sample, with a flux density limit at 325 MHz of 30 mJy and a limiting red magnitude of 16, can be constructed, which contains 119

We present bidimensional, long-slit spectroscopic mapping of the prototypical low-metallicity dwarf galaxy I Zw 18. A total of eight spaced slit positions were observed, covering most of the body of the galaxy and part of the extended envelope of the diffuse ionized halo seen in deep Hα images of I Zw 18. Spectroscopic maps of the galaxy have been