Data for five continuous years (1984 to 1989) at the Teide Observatory (Izaña, Tenerife), obtained with a full-disc solar multi-channel photometer devoted to the detection of solar intensity oscillations have now been used for a detailed study of the extinction coefficient behaviour at several wavelengths (450-870 nm) under different atmospheric

The outstanding quality of the Canarian sky, protected by law, makes it feasible to install the largest telescopes in the world at the observatories of the Instituto de Astrofísica de Canarias (IAC), which has promoted the design and construction of the Gran Telescopio Canarias (GTC). The GTC is a high-performance 10-m class telescope to be

We have obtained low-resolution optical spectra of three faint brown dwarf candidates in the Pleiades open cluster. The objects observed are Roque 12 (I_C=18.5), Roque 5 (I_C=19.7), and Roque 25 (I_C=21.2). The spectrum of Roque 25 does not show the strong TiO band heads that characterize the optical spectra of M-type stars, but molecular bands of

La interpretación de observaciones espectroscópicas detalladas de diversas estrellas revela inconsistencias, posiblemente debido a que las hipótesis utilizadas son inadecuadas. Los paralajes medidos por el satélite Hipparcos establecen un sistema de referencia sólido que se ha utilizado para comprobar la validez de los modelos de atmósfera clásicos

We present intermediate-resolution (FWHM~1.5-2.6 Angstroms) optical spectra of 106 candidate optical counterparts of 77 X-ray sources detected in four pointed (t_exp>=8700 s) ROSAT PSPC observations of the rho Ophiuchi star-forming region and vicinity. Using the spectral types and equivalent widths of Hα and Liilambda670.8 nm obtained from our

The following topics were dealt with: atmospheric optics, image quality, the Gran Telescopio Canarias project, site testing, meteorological effects, the Galileo Telescope, the Half Arcsecond Programme, the Nordic Optical Telescope, wide-field wavefront sensing, adaptive optics, JOSE site evaluation, the William Herschel Telescope, the Swedish