An uncrossed echelle spectrograph has been constructed in a collaboration between the Queen's University of Belfast and the Instituto de Astrofísica de Canarias for a series of joint investigations requiring very high spectral resolution observations (up to λ/Δλ ˜ 1O5). It is being used to observe stellar and interstellar lines over the wavelength

EL PRESENTE TRABAJO REPRESENTA UN PASO MAS EN LA BUSQUEDA DE ALGORIMOS POTENTES PARA PODER APROVECHAR TODA LA POTENCIA DE LOS TELESCOPIOS ACTUALES, DE GRANDES DIAMETROS, PERO LIMITADA RESOLUCION ESPACIAL, DEBIDO A LA INFLUENCIA ATMOSFERICA. LA OBTENCION DE IMAGENES DE ALTA RESOLUCION ESPACIAL ES UNO DE LOS PUNTOS DE MAYOR INTERES DE LA ASTROFISICA

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In this paper we present a new method to solve those radiative transfer problems where the scattering term in the source function, i.e., the frequency-integrated mean intensity J(phi), is independent of both frequencies and directions. This particular form of the source function, together with an implicit description of the evolution of the

We have observed the He I D3 λ 5876 Å line as a chromospheric activity indicator in 36 stars (34 F-type and 2 G-type) belonging to the Hyades open cluster, the Ursa Major group and the field. Complementing our data with measurements taken from the literature, we have correlated the equivalent width and absorbed energy flux of the He I line with

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