Flares and X-ray jets on the Sun arise in active regions where magnetic flux emerges from the solar interior amd interacts with the ambient magnetic field. The interactions are believed to occur in electric current sheets separating regions of opposite magnetic polarity. The current sheets located in the corona or upper chromosphere have long been

We follow, using both optical spectroscopy and photometry, the ``textbook'' colliding-wind WR+O binary WR 140 through and between the periastron passages of 1993 and 2001. An extensive collection of high-quality spectra allows us to derive precise orbital elements for both components simultaneously. We confirm the extremely high eccentricity of the

We present an IZ photometric survey covering a total area of about 1000 arcmin2 around the ɛ Orionis young massive star (˜10 Myr, d=412 pc) and reaching a limiting magnitude I=22. From the resulting I, I-Z color-magnitude diagram we have selected 123 red candidates in the interval I=15--22 mag, which according to evolutionary models corresponds to

The primordial abundance of 4He, YP, is one of the hottest themes in present-day astronomy, mostly due to its cosmological relevance. The disagreement between different determinations has been currently reduced to the 1-2% level, but these differences are still large enough to have deep implications for Big-Bang nucleosynthesis. It is therefore

We present J-H-K' photometry for a sample of 45 high redshift quasars found by the Sloan Digital Sky Survey. The sample was originally selected on the basis of optical colors and spans a redshift range from 3.6 to 5.03. Our photometry reflects the rest-frame SED longward of Lyalpha for all redshifts. The results show that the near-IR colors of high

We explore a scenario in which metal-poor globular clusters (GCs) are enriched by the first supernovae in the universe. If the first stars in a 107 Msolar dark halo were very massive (>180 Msolar), then a pair-instability supernova from a single massive star could produce sufficient iron to enrich 106 Msolar of pristine, primordial gas to [Fe/H]~-2