Aims:We calculate the dust emission expected at 3.43 and 3.53 μm if meteoritic (i.e. hydrogenated) nanodiamonds are responsible for most of the far-UV break observed in quasars. Methods: We integrate the UV flux that hydrogenated nanodiamonds must absorb to reproduce the far-UV break. Based on laboratory spectra of H-terminated diamond surfaces, we

We present a theoretical investigation on the influence of a deterministic magnetic field on the linear and circular polarization of the Na I, K I, and Ba II D2 lines. We describe the three ions by means of a three-level atomic model, and we take into account the hyperfine structure which is shown by some isotopes. We focus on the ``solar

Following the recently reported decline of the X-ray flux from the millisecond pulsar HETE J1900.1-2455 (Galloway et al. 2007, ATel #1086), we acquired images of its optical counterpart using the Wide Field Camera mounted on the 2.5m Isaac Newton Telescope at La Palma. The images were obtained on 2007 May 29 4:10-4:33 UT and May 30 3:42-4:17 UT and

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Proper motions in a sunspot group with a δ-configuration and close to the solar disk center have been studied by employing local correlation tracking techniques. The analysis is based on a more than 1 hr time series of G-band images. Radial outflows with a mean speed of 0.67 km s-1 have been detected around the spots, the well-known sunspots moats

We present ground-based B- and R-band color-magnitude diagrams (CMDs) reaching the oldest main-sequence (MS) turnoffs with good photometric accuracy for 12 fields in the Small Magellanic Cloud (SMC). Our fields, located between ~1° and ~4° from the center of the galaxy, are situated in different parts of the SMC such as the ``Wing'' area and toward