Observations of the 1400-1800 A region in late A type stars are presented, which were obtained using the IUE satellite at low and high resolution. The calibrated energy distribution is derived and presents a large variation with wavelength in the spectral range due to Si I photoionization discontinuities. Emission lines formed in the transition

Spectra from IUE of 6 main sequence and near main sequence stars from classes A5 to G8, between 2700 A and 2900 A wavelength are described. In toto, some 250 absorption lines are identified. Observed differences in those atomic and ionic multiplets present in each spectrum are shown to be due either to the regular progression in spectral class, or

This paper presents an alternative procedure which extracts spectra from IUE low resolution images. The -by-line image is scanned perpendicularly to the direction of dispersion . The resulting cross-cuts are then fitted with a known-form analytical function, which consists of a linear base-line describing the background plus as many bands as there

A model is given for constructing artificial integrated spectral lines which allows the inclusion of all effects relevant to the synthesis of these lines by numerical methods. Among the effects included are noise, limb darkening, the centre-to-limb variation of the shapes and wavelength positions of the spectral line profiles, different laws of the

PARTIENDO DE LOS ULTIMOS RESULTADOS EXPERIMENTALES SUMINISTRADOS POR LAS SONDAS ESPACIALES HELIOS A Y B ASI COMO DEL CONJUNTO DE MEDIDAS DE LA LUZ ZODIACAL OBTENIDAS DESDE OBSERVATORIOS TERRESTRES SE ESTABLECE POR PRIMERA VEZ UN ESQUEMA TEORICO DE LA DINAMICA DE LA MATERIA INTERPLANETARIA. DENTRO DE ESTE ESQUEMA SE ANALIZAN LAS DISTINTAS FUERZAS

From a measurement of the J = 3 - 2 rotational emission line of hydrogen isocyanide, and a literature value for that J = 1 - 0 line (Snell, 1979), the excitation parameters for HNC in the direction of the molecular peak as determined by CO were derived. Kinetic temperatures for the optically thick CO and (C-13)O transitions are about 50 K, while