P Cygni is a prototype for understanding mass loss from massive stars. This textbook star is known first of all because of two great eruptions in the 17th century. In the first half of this century it has given its name to a class of stars which are characterized by spectral lines consisting of nearly undisplaced emissions accompanied by a blue

We analyze optical images and high-resolution, long-slit spectra of three planetary nebulae that possess collimated, low-ionization features. NGC 3918 is composed of an inner, spindle-shaped shell mildly inclined with respect to the plane of the sky. Departing from the polar regions of this shell, we find a two-sided jet expanding with velocities

IAUC 7271 available at Central Bureau for Astronomical Telegrams.

IAUC 7267 available at Central Bureau for Astronomical Telegrams.

El objetivo de esta tesis es el estudio de la historia de formación de nuestra Galaxia. Para ello, hemos analizado los sistemas estelares más viejos, los cúmulos globulares, obteniendo como resultado principal el que esa formación e produjo mediante un colapso rápido del halo. La tesis se presenta en tres bloques principales. -En el primero se

The Hipparcos mission has made it possible to constrain the positions of nearby field stars in the colour-magnitude diagram with very high accuracy. These positions can be compared with the predictions of stellar evolutionary calculations to provide information on the basic parameters of the stars: masses, radii, effective temperatures, ages, and