Context: The variable pre-white dwarf PG 1159 stars (GW Vir) are g-mode non-radial pulsators. Asteroseismology puts strong constraints on their global parameters and internal structure. PG 0122+200 defines the red edge of the instability strip and its evolutionary timescale is predicted to be dominated by neutrino emission. Its study offers the

Aims:In light of recent contradictory observational results concerning the atomic polarization of solar H I lines, our purpose is to present certain collisional effects that might contribute towards a possible explanation. In particular, we aim to draw attention to the possibility of creating the "impact circular polarization". Methods: A general

IGR J00291+5934 is one of the seven accreting millisecond pulsars (AMPs) discovered so far. We report on the aperiodic timing and color analysis of its X-ray flux, using all the RXTE observations of the 2004 outburst. Flat-top noise and two harmonically related quasi-periodic oscillations, all of them at very low frequencies (0.01-0.1 Hz), were

The physical interpretation of spectropolarimetric observations of lines of neutral helium, such as those of the 10830 Å multiplet, represents an excellent opportunity for investigating the magnetism of plasma structures in the solar chromosphere. Here we present a powerful forward modeling and inversion code that permits either to calculate the

Accurate photometry with HST's ACS shows that the main sequence (MS) of the globular cluster NGC 2808 splits into three separate branches. The three MS branches may be associated with the complexities of the cluster's horizontal branch and of its abundance distribution. We attribute the MS branches to successive rounds of star formation, with

The spectroscopic observations were conducted during several runs spanning 15 years from March 1988 to June 2003. The observations from the Southern Hemisphere were carried out in most cases at the European Southern Observatory (ESO, La Silla, Chile) with the 1.5m ESO telescope, equipped with a Boller & Chivens spectrograph. The first and last runs