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

The study of the Balmer radial velocity curve of the cataclysmic variable (CV) VY Scl has revealed a new value for the orbital period (0.232 days), which significantly differs from the previously accepted one. It also shows a gamma modulation that is compatible with the presence of a third component, indicating that this object could be a

A catalog of a sample of 105 Jupiter family (JF) comets (defined as those with Tisserand constants T>2 and orbital periods P

The monitoring of the column density of atmospheric sodium could be crucial for the efficiency of LGS systems. However, its detection is affected by the presence of water lines around the sodium doublet lines; this is really dramatic in the D2 line. We have developed a new method to detect the D2 sodium telluric line, obtaining previously the solar