Rayleigh scattering produced in the lower atmosphere by laser launched from the ground, could be very relevant for performances of Laser Guide Stars systems and for light contamination measurements in other close telescopes. We have studied the scattering above Teide Observatory (Canary Islands) produced by a potassium laser. We show measurements

The abundance of Li in stars formed within the past 5 Gyr is logN(Li)=3.2(+/-0.2), while the corresponding value for the oldest stars in the Galaxy is logN(Li)=2.2(+/-0.2). The global evidence suggests that the latter represents the full, or the major, part of the primordial abundance, so that the difference of an order of magnitude is due to Li

Hierarchical clustering scenarios for galaxy formation predict that dwarf galaxies are the first to be formed and that they are building blocks of larger galaxies. We propose here to measure the spatial structure and the stellar age and metallicity distribution of the Phoenix dwarf galaxy to give support or reject such scenarios. The kind of

The PSF of a segmented mirror telescope is hardly affected by the segments alignment and it can cancel the performances of the Adaptive Optics Systems. The piston and tilt of each segment must be uniformly adjusted in relation to the rest of the segments. Furthermore, the direct detection of the alignment error with natural stars would be desirable

The results of two runs of time-series photometry made at the Nordic Optical Telescope clearly show that the sdB star PG 1618+563B is a new member of the EC 14026 class of sdB pulsators. Its power spectrum shows a doublet of frequencies at about 6.95 and 7.18 mHz (P ~ 144 and 139 s respectively), which produce a modulation effect in the light curve

We present optical photometry of the X-ray transient XTE J2123-058, obtained in 1998 July-October. The light curves are strongly modulated on the 5.95-h orbital period, and exhibit dramatic changes in amplitude and form during the decline. We used synthetic models, which include the effect of partial eclipses and X-ray heating effects, to estimate