A sample of 47 faint Gigahertz Peaked Spectrum (GPS) radio sources selected from the Westerbork Northern Sky Survey (WENSS) has been imaged in the optical and near-infrared, resulting in an identification fraction of 87 per cent. The R-IR-K colours of the faint optical counterparts are as expected for passively evolving elliptical galaxies

The interpretation of detailed spectroscopic observations of different stars reveals inconsistencies, due likely to inadequacies of the underlying hypothesis. The high accuracy of the parallaxes measured by the Hipparcos satellite established a firm reference frame that is used here to test theoretical classical model atmospheres for cool stars

The Hubble constant can be measured from the time delay between pairs of components of a multiply-imaged quasar, depending only on the mass model and the distances to the lens and background source. For a well-determined lens model, H_0 is implicitly related to the observable parameters by H_0 propto sigma_nu^2 Delta tau^{-1}, where sigma_nu is a

The synthetic color-magnitude diagram (CMD) methodology to study the star formation history (SFH) of nearby galaxies is briefly reviewed. Firstly the most significant features of the CMD for this task are discussed. Then, the procedure of computing synthetic CMDs is explained and the main results obtained by our group in the last few years

We present a test for the degree of symmetry in the distribution of the Hα brightness along the arms of a sample of spiral galaxies. The test consists of deriving the cross-correlation function of the Hα brightness as a function of curvilinear distance along pairs of opposed arms, after unfolding the arms geometrically. Our results reveal a

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