High-resolution optical spectra of eighteen blue horizontal-branch (BHB) stars in the globular cluster M15 indicate that their stellar rotation rates and photospheric compositions vary strongly as a function of effective temperature. Among the cooler stars in the sample, at Teff ∼ 8500K, metal abundances are in rough agreement with the canonical cluster metallicity, and the v sin i rotations ap...

We study the spatial distribution of Galactic metal-free stars by combining an extremely highresolution (7.8 × 10M⊙ per particle) Cold Dark Matter N-body simulation of the Milky-Way with a semi-analytic model of metal enrichment. This approach allows us to resolve halos with virial temperatures down to the 10K atomic cooling limit, and it is sufficiently flexible to make a number of robust conc...

As many as 109 neutron stars populate the Galaxy, but only ≈ 103 are directly observed as pulsars or as accreting sources in X–ray binaries. In principle also the accretion of the interstellar medium may make isolated neutron stars shine, and their weak luminosity could be detected in soft X–rays. Recent ROSAT observations have convincingly shown that neutron stars accreting from the interstell...

We have computed the galactic trajectories of twelve hypervelocity stars (HVSs) under the assumption that they originated in the Galactic Centre. We show that eight of these twelve stars are bound to the Galaxy. We consider the subsequent trajectories of the bound stars to compute their characteristic orbital period, which is 2 Gyr. All eight bound stars are moving away from the centre of the G...

We examine patterns of variation of 32 primarily main-sequence Sun-like stars [selected at project onset as stars on or near the main sequence and color index 0:42 (B V ) 1:4], extending our previous 7Y12 yr time series to 13Y20 yr by combining Strömgren b, y photometry from Lowell Observatory with similar data from Fairborn Observatory. Parallel chromospheric Ca iiH and K emission data from th...

Key words stars:chemically peculiar – stars:evolution – stars:magnetic fields – stars:fundamental parameters – stars:rotation – stars:statistics We re-discuss the evolutionary state of upper main sequence magnetic stars using a sample of Ap and Bp stars with accurate Hipparcos parallaxes and definitely determined longitudinal magnetic fields. We confirm our previous results obtained from the st...

In this review we concentrate on the dynamical evolution of the Milky Way as monitored in the solar neighbourhood. The relevant data sets are presented and discussed in detail. In the second part we review various mechanisms, which drive the dynamical evolution. 1. Dynamical evolution of the galactic disk traced in the solar neighbourhood The key data set, which we use for this study, is the Fo...

We propose a simple interpretation of the rotation period data for solarand late-type stars. The open cluster and Mt. Wilson star observations suggest that rotating stars lie primarily on two sequences, initially called I and C. Some stars lie in the intervening gap. These sequences, and the fractional numbers of stars on each sequence evolve systematically with cluster age, enabling us to cons...

1.1 Introduction Carbon stars are tracers of the intermediate age population in galaxies. Either they are currently undergoing third dredge-up on the (Thermal-Pulsing) Asymp-totic Giant Branch (TP-AGB) – the cool and luminous N-type carbon stars (or the " infrared carbon stars " , when they are significantly reddened by circumstel-lar dust through mass-loss) –, or have been enriched with carbon...