Based on photometry of deep CCD frames of the central region of the OB cluster Berkeley 86, we derive the cluster mass function. The absence of current star formation, and the cluster's young age of about 6Myrs, leads to the conclusion that the initial mass function (IMF) and the current mass function are identical for stars with m

In order to provide additional constraints to current models of angular momentum evolution of solar-type stars, we have conducted a period-determination program in the Alpha Perseus cluster. We have selected a sample of 22 Alpha Persei G and K dwarfs on the basis of their seemingly slow rotation rate (vsini

We present the first optical observations of the soft X-ray transient Nova Vela 1993, taken during quiescence in 1995 and 1996. From the R-band photometry with a mean magnitude of 20.6, we find an orbital, ellipsoidal modulation with an amplitude of 0.23 mag at a period of 6.86+/-0.12 h. The optical spectra show only broad double-peaked Hα emission

We have obtained broad-band optical spectra of a sample of 15 low-mass X-ray binaries (LMXBs) in the range 4000-9000A and fitted them with combinations of standard accretion disc models plus secondary star templates. For the sample of LMXBs in which we determine the power-law indices of the accretion disc flux distribution, we can explain the

We have developed a new stellar population synthesis model designed to study early-type galaxies. It provides optical and near-infrared colors, and line indices for 25 absorption lines. It can synthesize single age, single metallicity stellar populations, or follow the galaxy through its evolution from an initial gas cloud to the present time. The

We have monitored spectroscopically the classical T Tauri star UZ Tau East. Most observations were obtained with the Intermediate Dispersion Spectrograph at the Isaac Newton Telescope in La Palma Observatory. Several additional spectra were obtained with other telescopes at La Palma, ESO and Lick observatories. Radial velocities were measured via