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The origin of the abundance discrepancy, i.e., the fact that abundances derived from recombination lines are larger than those from collisionally excited lines, is one of the key problems in the physics of photoionized nebulae. In this work, we analyze and discuss data for a sample of Galactic and extragalactic H II regions where this abundance

Aims:We searched for very high energy (VHE) γ-ray emission from the supernova remnant Cassiopeia A Methods: The shell-type supernova remnant Cassiopeia A was observed with the 17 m MAGIC telescope between July 2006 and January 2007 for a total time of 47 h. Results: The source was detected above an energy of 250 GeV with a significance of 5.2σ and

Context: Classical T Tauri stars are young solar-type stars accreting material from their circumstellar disks. Thanks to a favorable inclination of the system, the classical T Tauri star AA Tau exhibits periodic optical eclipses as the warped inner disk edge occults the stellar photosphere. Aims: We intend to observe the X-ray and UV emission of AA

We present IPHAS positions and photometry for 4853 sources selected as having a Hα excess from the photometry. The catalogue covers the magnitude range 13

We present observations of magnetic fields of the very quiet Sun near disk center using the Spectro-Polarimeter of the Solar Optical Telescope aboard the Hinode satellite. These observations reveal for the first time the ubiquitous presence of horizontal magnetic fields in the internetwork regions. The horizontal fields are spatially distinct from