We report our analysis of the stability of pulsation periods in the DAV star (pulsating hydrogen atmosphere white dwarf) ZZ Ceti, also called R 548. Based on observations that span 31 years, we conclude that the period 213.132605 s observed in ZZ Ceti drifts at a rate dP/dt=1.2 Gyr, comparable to the theoretical cooling timescale for the star. Our

The plans for the commissioning of the GTC are being drawn up at the GTC Project Office. The commissioning will start before first light, with the commissioning of the telescope mount and will continue until after normal science operations begin. The aim of the commissioning is to convert a series of subsystems into a single instrument that is

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In this contribution we analize the chemical and rotational properties of a sample of hot HB stars in the globular clusters M15 M79 M80 and NGC 2808 with effective temperatures Teff between 7000 K and 25000 K. To this purpose we have used high resolution spectroscopy with UVES+VLT. Our study reveals the existence of a discontinuity in the

We present high resolution spectroscopic data of the two giant extragalactic HII regions NGC 5461 and NGC 5471 in M 101. We calculate the physical conditions in the two nebulae with a large number of diagnostics, and determine their chemical abundances by applying ionization correction factors (ICFs) to the observed ionic abundances. The comparison

Microvariations (magnitude changes of several hundredths in timescales ranging from minutes to hours) may arise from three sources: jet and accretion instabilities and gravitational microlensing events. Each may produce different changes on the quasars continuous spectra. For this reason, BVR observations can yield a high degree of discrimination