We present synthetic optical spectra in the red and far-red (640-930 nm) of a sample of field L dwarfs suitably selected to cover this new spectral class, and the brown dwarf GL 229B. We have used the recent ``dusty'' atmospheres by Tsuji (cite{tsuji00}) and by Allard (cite{allard99}), and a synthesis code (Pavlenko et al. cite{pav95}) working

On March 2 06:00 UT the transient source XTE J1859+226 had faded considerably to R=18.0 in the optical (IAC) and to a flux of about 13 mCrab (RXTE ASM). However, it clearly remains active in the X-rays. From extrapolating the last spectrum obtained with HST on 2000, February 8th we predict the following approximate magnitude and colours: V~18.4, U

Not Available

We present R-band photometry of the SW Sex-type cataclysmic variable WX Arietis made in October 1995 and August 1998-February 1999. Contrary to previous results, we find that WX Ari is an eclipsing system with an orbital inclination of i =~ 72o. The R-band light curves display highly variable, shallow eclipses ~ 0.15-mag deep and =~ 40 min long

Sub-arcsecond JHK images of the star formation region NGC 6334 IV covering 14.7arcmin2 have been obtained. These were supplemented by H2 and Brγ images of the central 2arcmin2. A total of 1238sources brighter than K=~17 were detected. Due to the very high extinction in this region, only 685 of these are brighter at 1.2μm than our limit, J=~20. Only

La espectroscopía bidimensional con fibras ópticas es una técnica reciente que permite obtener simultáneamente la información espacial y espectral de un objeto extenso. Esta técnica puede ser aplicada en varios campos de la Astrofísica como, p.e., las regiones circumnucleares de galaxias. En esta Tesis analizamos los resultados obtenidos en esta