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

We have used photometric images of 10 barred galaxies in the B and I bands to infer geometric and dynamical parameters of their bars: their lengths, their strengths, and their corotation radii. The bar length, R_bar, is measured as the radius at which the odd Fourier components of the I image show a rise, accompanied by a blue peak in the B-I

We present optical spectroscopy and optical and infrared photometry of the neutron star soft X-ray transient Aql X-1 during its X-ray outburst of 1997 August. By modelling the X-ray, optical and IR light curves, we find a 3-d delay between the IR and X-ray rise times, analogous to the UV-optical delay seen in dwarf novae outbursts and black hole X