We present high-quality (subarcsecond) optical narrowband CCD images of the planetary nebula NGC 6881, which reveal a highly collimated bipolar structure. A careful examination of the [N II] image and of the [N II]/[O III] and [N II]/Hα ratio images shows that NGC 6881 is a quadrupolar planetary nebula, that is, a twice bipolar planetary nebula

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

The velocity field of the nearly face-on galaxy NGC 3631 is derived from observations in the Hα line on the 6-m telescope of the Special Astrophysical Observatory. These optical data are compared with radio observations of this galaxy (Knapen 1997). It is argued that the two-armed spiral structure of NGC 3631 has a wave nature, and that the

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 observations and analyses of some of the most massive stars in the Milky Way, showing the potential and limits of current model atmospheres, and the consequences for the evolution theory of massive stars. We then show how these techniques can be applied to very bright stars in M31 and M33 to derive radial abundance gradients and get

To preserve the exceptional sky quality of the Roque de Los Muchachos Observatory, the Spanish Government has subsidized the cost of a programme of streetlighting adaptation on La Palma aimed at minimizing potential light pollution. New non-polluting light fixtures and low-pressure sodium vapour lamps have been used to modified existing lighting