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

The study of the IR emission from Seyfert galaxies is of key importance for understanding the origin of the extraordinary nuclear activity seen in these objects as well as the differences between the various Seyfert types. Two important problems remain unresolved. For instance, whether the IR radiation from Seyfert galaxies is of mostly thermal or

We have digitally co-added APM scans of 13 Kodak TechPan films of the SE region of the Virgo cluster of galaxies. The ~ 6.2degr x 6.2degr field of the R-band films combined with the resolution of ~ 2 arcsec pixel(-1) results in data file sizes of about 222 MBytes. The 13 scanned films have been aligned, co-added, corrected for vignetting effects