The population of high-energy and very high-energy γ-ray sources, detected with EGRET and the new generation of ground-based Cherenkov telescopes, forms a reduced but physically important sample. Most of these sources are extragalactic (e.g. blazars), while among the galactic ones there are pulsars and supernova remnants. The microquasar LS 5039

Observations of binary stars containing an accreting black hole or neutron star often show x-ray emission extending to high energies (>10 kilo­–electron volts), which is ascribed to an accretion disk corona of energetic particles akin to those seen in the solar corona. Despite their ubiquity, the physical conditions in accretion disk coronae remain

A technique for obtaining an ideal two-mirror coude system with no instrumental polarization is described. A half-wave plate positioned between the two mirrors with the proper orientation produces the desired effect. The level of spurious polarization is limited by the characteristics of the retarder and the similarity of the mirrors. The telescope

Aims. We search for brown dwarfs at the Class 0/I evolutionary stage, or proto brown dwarfs. Methods: We present a multi wavelength study, ranging from optical at 0.8 μm to radio wavelengths at 6 cm, of a cool, very faint, and red multiple object, SSTB213 J041757, detected by Spitzer toward the Barnard 213 dark cloud, in Taurus. Results: The SED of

The radio properties of low surface brightness (LSB) dwarf galaxies are still largely unknown. To help remedying this situation we observed twelve LSB dwarfs with the VLA at lambda = 3.6 cm and lambda = 20 cm. All galaxies are included in the UGC catalog and have previously claimed radio continuum detections at either 21 cm (Altschuler et al. 1984

A detailed insight into the star formation history of a sample of HII galaxies has been obtained, based on radio continuum and optical broad band and narrow band observations. HII galaxies are dwarf galaxies whose optical spectrum resembles that of HII regions, many of which are also known as Blue Compact Dwarf Galaxies. VLA observations at several