Related papers: The Binary Second Sequence in Cluster Colour--Magn…
We report about an ongoing photometric and spectroscopic monitoring survey of about 250 O- and 540 B-type stars in the southern Milky Way with the aim to determine the fraction of close binary systems as a function of mass and to determine…
Globular clusters (GCs) display much lower binary fractions than found among main-sequence stars in the solar neighborhood. The physical cause of this difference is debatable: does it reflect different star formation outcomes at low…
The formation of massive stars in close binary systems is complicated due to their high radiation pressure, the crowded environment and the expected minimum separation for fragmentation being many times greater than the orbital separation.…
The majority of the inhomogeneities in the chemical composition of Globular Cluster (GC) stars appear due to primordial enrichment by hot-CNO cycled material processed in stars belonging to a first stellar generation. Either massive AGB…
Massive stars are known to have a high multiplicity, with examples of higher order multiples among the nearest and best studied objects. In this paper we study hierarchical multiple systems (an inner binary as a component of a wider binary)…
Disentangling distinct stellar populations along the red-giant branches (RGBs) of Globular Clusters (GCs) is possible by using the pseudo two-color diagram dubbed chromosome map (ChM). One of the most intriguing findings is that the…
We propose that the observed difference in the formation rates of bright low-mass X-ray binaries in metal-rich and metal-poor globular clusters can be explained by taking into account the difference in the stellar structure of main sequence…
Massive stars are among the most important objects in the Universe and many (most?) of them are formed in binaries. A selection of observational and theoretical facts that illustrate the importance of binaries and the evolution of massive…
Observations of galactic and extra-galactic globular clusters have shown that on average metal-rich clusters are ~3 times as likely to contain a bright X-ray source than their metal-poor counterparts. We propose that this can be explained…
High-precision multi-band HST photometry reveals that the main sequence (MS) of the globular cluster NGC 6397 splits into two components, containing ~30% and ~70% of the stars. This double sequence is consistent with the idea that the…
The discovery of multiple stellar populations in globular clusters raises fundamental questions concerning the formation and dynamical history of these systems. In a previous study aimed at exploring the formation of second-generation (SG)…
Two colour photometry of the cluster A1689 reveals a `relative magnification-bias' between lensed blue and red background galaxies, arising from a dependence of the faint galaxy count-slope on colour. The colour distribution is skewed…
Recent, high precision photometry of Omega Centauri, the biggest Galactic globular cluster, has been obtained with Hubble Space Telescope. The color magnitude diagram reveals an unexpected bifurcation of colors in the main sequence (MS).…
Star clusters with a high central density contain an ecological network of evolving binaries, affected by interactions with passing stars, while in turn affecting the energy budget of the cluster as a whole by giving off binding energy.…
We present HST observations that show a bifurcation of colors in the middle main sequence of the globular cluster Omega Centauri. We see this in three different fields, observed with different cameras and filters. We also present high…
We examine the dynamical destruction of binary systems in star clusters of different densities. We find that at high densities (10^4 - 10^5 Msun pc^-3) almost all binaries with separations > 10^3 AU are destroyed after a few crossing times.…
Lensing in the context of rich clusters is normally quantified from small image distortions, yielding a relative mass distribution in the limit of weak lensing. Here we show the magnification effect of lensing can also be mapped over a…
We investigate the clustering of galaxy groups and clusters in the SDSS using the Berlind et al. (2006) group sample, which is designed to identify galaxy systems that each occupy a single dark matter halo. We estimate group masses from…
We explore the effects of dynamical evolution in dense clusters on the companion mass ratio distribution (CMRD) of binary stars. Binary systems are destroyed by interactions with other stars in the cluster, lowering the total binary…
The presence of multiple stellar populations in globular clusters leads to a complex dynamical environment that significantly influences the evolution of binary stars, which in turn impacts the evolution of the cluster itself. For this…