We present a review on the determination of the primordial helium abundance, Y_p, based on the study of hydrogen and helium recombination lines in extragalactic H II regions. We also discuss the observational determinations of the increase of helium to the increase of oxygen by mass Δ Y/Δ O , and compare them with predictions based on models of

A method to obtain the Duvall phase function from the structure of a stellar model is presented. This can be a good tool for understanding the dependence of p-mode frequencies on the structure of the upper layers of the convection zone. A linear relation between phase function differences of two models and their equilibrium structure differences is

New accurate and homogeneous optical UBVRI photometry has been obtained for variable stars in the Galactic globular cluster ω Cen (NGC 5139). We secured 8202 CCD images covering a time interval of 24 years and a sky area of 84 × 48 arcmin. The current data were complemented with data available in the literature and provided new, homogeneous

We have obtained the best fit to the light profiles of a luminosity- limited sample of elliptical and S0 galaxies with a power law r^1/n^, letting the exponent remain free rather than keeping it fixed at 1/n = 1/4 as in the well-known de Vaucouleurs formula. The introduction of a free parameter in the fitting formula (ranging from n = 0.5 for (r_e_

We present new evidence against the universality of the de Vaucouleurs r^1/4^ law, considered to be the best empirical formula for fitting the light profiles of elliptical galaxies, through the analysis of the properties of the (D_n_/A_e_)-_e_ diagram for a volume-limited sample of early-type galaxies that are members of the Virgo and Fornax