Seeing statistics from several year-long site-testing campaigns carried out at different locations at the Roque de los Muchachos Observatory (ORM) are reviewed (this contribution contains results previously published by Munoz-Tunon et al. (1997) [Estudio de Sitio para el Gran Telescopio: Informe final; A&AS, 125, 183]). In particular, tests at the

We present monthly statistics for a two-year meteorological site-testing campaign at the two candidate sites for the location of the GTC. The windroses presented here are a fairly complete representation of the wind regimes prevailing at the lower site and indicate that at night the predominant wind direction for the site is from the NE, whereas

We present echelle spectroscopy in the 3500 to 10300AA range of the Hourglass Nebula which is embedded in the galactic HII region M8. The data were obtained using the 2.1 m telescope at Observatorio Astronomico Nacional in San Pedro Martir, Baja California. We have measured the intensities of 274 emission lines, in particular 88 permitted lines of

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^