Aims:We study the contradictory magnetic field strength distributions retrieved from independent analyses of spectropolarimetric observations in the near-infrared (1.56 μm) and in the visible (630 nm) spectral ranges in internetwork regions. Methods: To solve this apparent controversy, we present simultaneous and co-spatial 1.56 μm and 630 nm

Aims:We study the properties and nature of extremely red galaxies (ERO, R-K≥5.6) found behind two lensing clusters and compare them with other known galaxy populations. Methods: New HST/ACS, Spitzer (IRAC and MIPS), and Chandra/ACIS observations of the two lensing clusters Abell 1835 and AC114 have been obtained, combined with our earlier optical

We report on new nearby L and late-M dwarfs (dphot = 3.0, later than M8.0) at low Galactic latitude (|b| 15°) over 4800 deg2 in the Deep Near Infrared Survey of the Southern Sky (DENIS) data base. We used late-M (>= M8.0), L and T dwarfs with accurate trigonometric parallaxes to calibrate the MJ versus I-J colour-luminosity relation. The resulting

Non-LTE effects affect the formation of many spectral features in the spectra of late-type stars. This thesis investigates the effect on carbon and oxygen abundances. The non-LTE calculations have been performed with the code MULTI, using MARCS atmospheric models with 4500

Boxy/peanut bulges in disc galaxies have been associated to stellar bars. We analyse their properties in a large sample of $N$-body simulations, using different methods to measure their strength, shape and possible asymmetry, and then inter-compare the results. Some of these methods can be applied to both simulations and observations. In particular

We demonstrate that low-resolution CaII triplet (CaT) spectroscopic estimates of the overall metallicity ([Fe/H]) of individual red giant branch (RGB) stars in two nearby dwarf spheroidal galaxies (dSphs) agree to +/-0.1-0.2 dex with detailed high-resolution spectroscopic determinations for the same stars over the range -2.5 [Fe/H] -0.5. For this