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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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Low and high resolution IUE spectra (1150-3200 Angstroms) of SN 1993J in NGC 3031 were obtained starting on 1993 March 30.2 UT. The initially strong ultraviolet continuum faded rapidly by April 4 (a factor of 200 at lambda

A morphological description and CCD photometric information for a sample of 24 low luminosity radio galaxies with radio jets are presented. It is concluded that Fanaroff-Riley type I low luminosity radio galaxies inhabit regions of higher galaxy density than radio-quiet ellipticals and powerful radio sources, and are more luminous in the optical