Related papers: Terzan 5: an alternative interpretation for the sp…

We have obtained deep BVI CCD photometry of Phoenix, a galaxy considered a transition case between dwarf spheroidal and dwarf irregular galaxies. A comparison of our data with the RGBs of Galactic globular clusters gives a mean metal…

It is now widely accepted that globular cluster red giant branch stars owe their strange abundance patterns to a combination of pollution from progenitor stars and in situ extra mixing. In this hybrid theory a first generation of stars…

We present an analysis of optical and ultraviolet Hubble Space Telescope photometry for evolved stars in the core of the distant massive globular cluster NGC 2419. We characterize the horizontal branch (HB) population in detail including…

The most massive Galactic globular cluster omega Cen appears to have two, or perhaps more, distinct main sequences. Its bluest main sequence is at the centre of debate because it has been suggested to have an extremely high helium abundance…

Theoretical integrated broad-band colors ranging from far-UV to near-IR have been computed for old stellar systems from our evolutionary population synthesis code. These models take into account, for the first time, the detailed systematic…

Recent work, based on data from the Hubble Space Telescope (HST) UV Legacy Survey of Galactic Globular Clusters (GCs), has revealed that all the analyzed clusters host two groups of first- (1G) and second-generation (2G) stars. In most GCs,…

We derive ages, metallicities and [alpha/Fe] ratios from the integrated spectra of 23 globular clusters in M31, by employing multivariate fits to two stellar population models. In parallel we analyze spectra of 21 Galactic globular clusters…

Photometry with HST's ACS reveals that the subgiant branch (SGB) of the globular cluster NGC 1851 splits into two well-defined branches. If the split is due only to an age effect, the two SGBs would imply two star formation episodes…

It has been proposed that the globular cluster-like system Terzan 5 is the surviving remnant of a primordial building block of the Milky Way bulge, mainly due to the age/metallicity spread and the distribution of its stars in the…

We exploit the large number of archival HST images of 47 Tuc to examine its subgiant branch (SGB) and main sequence (MS) for signs of multiple populations. In the cluster core, we find that the cluster's SGB exhibits a clear spread in…

The horizontal branch (HB) morphology of globular clusters (GCs) is mainly described by metallicity. The fact that some clusters with almost the same metallicity exhibit different HB demonstrates that other parameters are at work. We…

We present a study of Far Ultraviolet (FUV) bright horizontal branch (HB) stars to understand the peculiarities seen in the HB sequence of the Globular Cluster NGC 1851, using ground and space based multi-wavelength data. Optical and UV…

We present high-resolution optical and near-infrared HST observations of two adjacent regions in the fossil starburst region in M82, B1 and B2. Age estimates date the cluster population in the fossil starburst between ~2 x 10^8 and ~10 x…

Most Globular Clusters so far examined host (at least) two stellar populations. This feature requires a two--step process, in which the nuclearly processed matter from a first generation (FG) of stars gives birth to a second generation (SG)…

If NGC 6397 contains a large fraction of "second generation" stars (>70% according to recent analysis), the helium abundance of its stars might also be affected, show some star-to-star variation, and be larger than the standard Big Bang…

We combine ground and space-based photometry of the Galactic globular cluster 47 Tuc to measure four independent lines of evidence for a helium gradient in the cluster, whereby stars in the cluster outskirts would have a lower initial…

We revisit the "second parameter" pair of globular clusters NGC 288/NGC 362 on the basis of theoretical models for red giant branch (RGB) and horizontal branch (HB) stars. The results of the most extensive set of RGB/HB simulations computed…

By means of grid-based, 3D hydrodynamical simulations we study the formation of second generation (SG) stars in a young globular cluster (GC) of mass 10^7 Msun, the possible progenitor of an old GC with a present mass ~(1-5) * 10^6 Msun.…

Globular clusters are old stellar systems which exhibit very-high stellar densities in their cores. The globular cluster Terzan 5 is characterized by a high stellar encounter rate and hosts the largest detected population of millisecond…

We report results from HST-NICMOS imaging of the extremely dense core of the globular cluster Terzan 5. This highly obscured bulge cluster has been estimated to have one of the highest collision rates of any galactic globular cluster,…