The mathematical structure of nonlinear, isentropic longitudinal flows of an ideal magnetohydrodynamic plasma confined to a magnetic flux tube embedded in a quiescent nonmagnetic fluid is investigated. Exact analytical solutions are derived for a special type of nonlinear flow in the absence of gravity: the simple waves, for which all the unknowns

Non-LTE calculations of H-alpha line profiles are presented and applied to derive rotational velocities from high-resolution spectra of DA white dwarfs. This paper extends recent work by Pilachowski and Milkey (1984, 1987) to southern hemisphere objects and confirms their findings that all white dwarfs seem to be slow rotators. Of the seven objects

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EN ESTE TRABAJO OBTENGO Y ANALIZO ESPECTROS DE LOS PARAMETROS DE STOKES V E I TOMADOS SOBRE PUNTOS BRILLANTES (EN CAII K) DE FACULAS Y RED FOTOSFERICA. PRESTO ESPECIAL ATENCION A LA INFLUENCIA DE LA POLARIZACION INSTRUMENTAL. POR ESTE MOTIVO NECESITO CALCULAR LA MATRIZ DE MUELLER DEL TELESCOPIO VGT DEL OBSERVATORIO DEL TEIDE. PONGO UN LIMITE

Monochromatic extinction coefficients at four wavelengths have been obtained over a period of more than two years at the Observatorio del Teide (Izaña Tenerife) using a full disc, direct sunlight, quadruple photometer devoted to the detection of integral luminosity oscillations of the Sun. The mean extinction coefficients (0.13 at 500 nm) show a

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