We argue on the basis of astrometric and spectroscopic data that the ultramassive white dwarf GD50 is associated with the star formation event that created the Pleiades and is possibly a former member of this cluster. Its cooling age (~60 Myr) is consistent with it having evolved essentially as a single star from a progenitor with a mass M >

We present a parallax measurement for the very cool degenerate WD 0346+246, the serendipitous discovery of which was reported by Hambly et al. We find an absolute parallax of 36+/-5mas, yielding a distance estimate of 28+/-4pc. The resulting absolute visual magnitude of the object is MV=16.8+/-0.3, making it the second-lowest luminosity white dwarf

We have compiled a catalogue of light curve solutions of contact binary stars. It contains the results of 159 light curve solutions. The properties of contact binary stars were studied using the catalogue data. As is well known since Lucy's (\cite{Lucy68a},b) and Mochnacki's (\cite{Mochnacki81}) studies, primary components transfer their own energy

We have obtained both virial and dynamical masses of a sample oflocal star forming galaxies from the UCM survey. The rotational curvesmeasured using the kinematics of the ionized gas where used as tracersof the mass of the system. The goal is to obtain a relationship with fotometric stellar masses,calculated from population synthesis models, in

This thesis is made of three main parts. In the first one a sample of 55 galaxies with an active nucleus (Seyfert 1, Seyfert2 and LINERs) is analysed; these were observed with the 4.2m WHT and 1m JKT in CCD narrow band H-alpha +[NII] and [OIII] to map the distribution of HII regions and the morphology of the circumnuclear extended emission

Microvariations probe the physics and internal structure of quasars. Unpredictability and small flux variations make this phenomenon elusive and difficult to detect. Variance-based probes such as the C and F tests, or a combination of both, are popular methods to compare the light curves of the quasar and a comparison star. Recently, detection