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

The data set presented here consists of 5 VLBI images at 86GHz taken with the Global mm VLBI Array (GMVA, and its predecessor, the CMVA) covering the time range from October 2001 to April 2004, and 34 Very Long Baseline Array (VLBA) images taken at 43GHz from June 1997 to February 2007. Among these 34 images, 20 obtained from June 1997 to May 2002