We explore the behaviour of the most popular spectroscopic absorption features in the optical region as a function of the initial mass function (IMF), while taking into account the spectral resolution and galaxy velocity dispersion. We conclude that the IMF produces a negligible effect on the Lick indices contained in the wavelength interval λ 3800

High resolution observations of interstellar Na I absorptions in the spectra of early-type stars in the second Galactic quadrant have been used to derive the spatial distribution of the nearby interstellar gas in the Galactic anticentre hemisphere. The data show the presence, within the region explored and within the nearest 150 pc, of eight

The distribution on the sky of clusters of galaxies shows significant association with relatively nearby, large, active galaxies. The pattern is that of clusters paired equidistant across a central galaxy with the apparent magnitudes and redshifts of their constituent galaxies being closely matched. The clusters and the galaxies in them tend to be

We investigate current problems in obtaining reliable ages for old stellar systems based on stellar population synthesis modeling of their integrated spectra. In particular, we address the large ages derived for the globular cluster 47 Tuc, which is at odds with its color-magnitude diagram (CMD) age. Using a new age indicator, Hγσ

We present high-resolution echelle spectroscopy of a sample of H II galaxies. In all galaxies we identify different Hα-emitting knots along the slit crossing the nucleus. All of these have been isolated and separately analyzed through luminosity and size versus σ diagnosis plots. We find that in all cases, for a particular galaxy, the bulk of the

Mid-infrared images of the Seyfert 1 galaxy Mrk 279 obtained with the ISO satellite are presented together with the results of a one-year monitoring campaign of the 2.5-11.7μm spectrum. Contemporaneous optical photometric and spectrophotometric observations are also presented. The galaxy appears as a point-like source at the resolution of the