The goal of this project is to analyze the integrated-light spectrum of a region in the LMC bar, for which HST images are already available yielding color-magnitude diagrams reaching the oldest main-sequence turnoff. Then, we can derive the star formation history in this field through evolutionary/population synthesis of the integrated light from

The photometric decay of sunspots is studied in some detail. Aspects related to leader vs. follower sunspot decay are presented and our current understanding of the physical mechanisms involved critically reviewed. The intrinsic instability of follower spots to form a stable sunspot cannot be understood in terms of the fluting stability as proposed

The probabilistic nature of the IMF in stellar systems implies that clusters of the same mass and age do not present the same unique values of their observed parameters. Instead they follow a distribution. We address the study of such distributions in terms of their confidence limits that can be obtained by evolutionary synthesis models. These

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Recent determinatios of baryonic density using the angular power spectrum of the Cosmic Microwave Background are very close to the classical estimate from Big Bang Nucleosynthesis. This reinforces the case for dark baryons in the Universe and for a large component of exotic cold dark matter. Present-day baryons can be hidden in substellar objects

En esta tesis se aborda el estudio de los espejismos gravitatorios QSO 0957+561 y QSO 2237+0305. Para ello se ha realizado un seguimiento fotométrico de 5 años del sistema QSO 0957+561 en el telescopio IAC-80 del Observatorio de Teide. Utilizando una nueva técnica de reducción fotométrica y un nuevo método de obtención del retraso temporal, se ha