Coordinated multifrequency observations of the dwarf nova SS Cygni have been performed for several years in order to study the accretion behavior of this system in particular and in general to clarify this crucial problem for cataclysmic variables. From IUE measurements, together with those from optical and IR ground based telescopes, orbital

The behavior of the elemental depletions in the ISM along lines of sight with a very low value of the average hydrogen density is examined. A simple model in the frame of the McKee-Ostriker (1977) theory has been used to estimate the line-of-sight filling factors as a function of n-bar for those interstellar phases in which a significant degree of

Complete infraredJ andK light curves of the RS CVn system XY UMa have been obtained at the beginning of 1989. We point out some interesting morphological changes observed in these light curves.

New infrared photometry of a sample of 39 stars in the open cluster NGC 752 is presented. These observations confirm the bimodality of the main sequence previously reported. The nature of this behavior is analyzed on the basis of the binary hypothesis.

Preliminary results on new CCD photometry inV andB bands of approximately 5000 stars in four overlapping fields in the globular cluster M3 are presented. The colour-magnitude diagram shows a very well-defined sequence with a small scatter, going fainter than previously published work on this cluster. The turn-off point found atV=19.1±0.2 mag and (B

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