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We present near-infrared photometry and optical spectroscopy of very low mass stars and brown dwarf candidates in the Pleiades open cluster. The membership status of these objects is assessed using color-magnitude diagrams, lithium and spectral types. Eight objects out of 45 appear to be nonmembers. A search for companions among 34 very low mass

Context. Binary systems experiencing one or two common envelope episodes during the red giant branch or the Hertzsprung gap phases can produce a single star, evolving along the Hayashi track, as a final outcome. Even if these objects are expected to be very common in nature, a proper description of their evolution and physical properties is still

The experimental study of sodium layer is relevant to fields such as adaptive optics, in particular for laser guide star generation. We have developed an instrument to make systematic measures of the most relevant parameters of the sodium layer above canarian observatories. The measurement provides information about sodium layer: the medium

IUE spectra of Mg II h and k in late type dwarfs and giants were used to detect and measure absorption components due to the LISM. This technique gives a method of probing the awkward range from d = 3 pc to d = 80 pc from the Sun. In spite of interpretational uncertainties the HI component of the LISM can be plotted well enough to confirm it as a

Simple gravitational lens models usually suffice to reproduce the positions of lensed quasar images, but they have problems to reproduce their optical flux ratios. The so-called flux ratio anomalies are thought to be produced by small-scale structure in the lens galaxies (microlensing).