A method for ``time/frequency'' analysis is shortly described, with a discussion of its limitations in time and frequency resolution, and in sensitivity to noise in the signal. This is then applied to observational data. The data used are the luminosity measurements of the IPHIR experiment, and the velocity measurements performed at the

In this paper we present new chemo-spectro-photometric models of elliptical galaxies in which infall of primordial gas is allowed to occur. They aim to simulate the collapse of a galaxy made of two components, i.e. luminous material and dark matter. The mass of the dark component is assumed to be constant in time, whereas that of the luminous

A systematic structuring of magnetic fields over scales much smaller than the mean free path of photospheric photons may be responsible for the observed asymmetrical Stokes profiles. We explore this possibility by deriving the radiative transfer equation for microstructured magnetic atmospheres (the MISMA approximation). This equation is

We show that the alteration between intervals of cyclic activity and grand minima like the Maunder minimum in the 17th century, which is characteristic for the long-term variation of the solar activity, can be described as on-off intermittency arising in a dymano driven by the instability of magnetic flux tubes in the overshoot layer below the

LMC-SMP83 is a planetary nebula in the Large Magellanic Cloud whose central star is recently reported by Pena et al. to show decreases in temperature and luminosity of at least 50% over a time span of seven years. Serendipitously, this object is observed with the Planetary and Faint Object Cameras onboard the Hubble Space Telescope between 1991

EL TRABAJO RECOGIDO EN LA PRESENTE MEMORIA SE BASA EN OBSERVACIONES REALIZADAS CON EL FOTOMETRO LOI-T INSTALADO EN EL OBSERVATORIO DEL TEIDE. SE ESTABLECE UN PROCEDIMIENTO PARA EL ANALISIS DE LOS DATOS, CALCULO DE LOS FILTROS OPTIMOS PARA LA IDENTIFICACION DE LOS MODOS, MEDIDA DE FRECUENCIAS, ANCHURAS, AMPLITUDES Y DESDOBLAMIENTO ROTACIONAL. EN SU