Strong Langmuir turbulence effects are investigated during ionospheric modification experiments performed at the Arecibo Observatory. Indirect evidence of Langmuir wave collapse is obtained through the observation of theoretically predicted 'caviton-type' enhanced plasma wave spectra. A typical spectrum consists of a 'free-mode' peak with a

EN EL PRESENTE TRABAJO, SE PONE DE RELIEVE LA NECESIDAD DE REVISAR CONCEPTON QUE USUALMENTE SE EMPLEAN EN LA INTERPRETACION DEL ESPECTRO SOLAR. EN PARTICULAR, SE MUESTRA QUE LA PROFUNDIDA MEDIA DE FORMACION DE UNA LINEZ ESPECTRAL, FRECUENTEMENTE EMPLEADA COMO ELEMENTO DE DIAGNOSTICO, NO TINE ESPECIAL INTERES PARA LA ASIGNACION DE UNA MEDIDA DADA A

We present the results of a spectroscopic analysis of 25 galactic luminous OB stars. The gravities are in general lower than previously assumed, especially for giants. The helium abundances are also higher than normal in many cases. Using data from the spectroscopic analysis, radii, luminosities and masses are derived. The observed wind terminal

We present a technique to model the instrumental polarization in the focal plane of a telescope. It takes into account that different rays of an incoming beam suffer different variation of the original polarization in their paths through the system. It also considers that the net effect depends on the way in which the different rays interfere with

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The discovery of lithium in the spectrum of the binary system V404 Cygni is described. A high lithium abundance in the secondary star, close to that of very young stars, is derived. Without lithium production, the secondary would have to be comparable in age to the Pleiades cluster. If the system is not being seen at an early moment in its lifetime