Aims: We investigate the relationship between the photospheric magnetic field and the emission of the mid chromosphere of the Sun. Methods: We simultaneously observed the Stokes parameters of the photospheric iron line pair at 630.2 nm and the intensity profile of the chromospheric Ca II H line at 396.8 nm in a quiet Sun region at a heliocentric

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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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