Found 16 talks width keyword globular clusters

The classical idea that globular clusters are the prototypes of simple stellar populations has been revolutionized in the last few years. Multiple sequences of stars have been detected in the colour-magnitude diagram of a number of clusters, mostly thanks to high-precision HST photometry, and the correlation with the chemical properties of different generations of stars has been demonstrated. In this talk, we will first present a summary of the observational picture, and we will then introduce the SUMO project (a SUrvey of Multiple pOpulations). This is a long-term project, lead here at the IAC and aimed at detecting and characterizing multiple populations in a large sample of globular clusters. We will review the scope, the observing and reduction strategy, and the first results. So far, data for more than 30 clusters have been secured, using the wide field imagers available at the 2.2m ESO/MPI and INT telescope, thus covering both hemispheres. We will present a new photometric index which turned out to be very effective in detecting multiple RGBs in nearly all the clusters analyzed so far. The connection with the chemical content of the different populations will be also discussed.

In the Λ-CDM galaxy formation paradigm, the star formation history of a galaxy is coupled to the total mass of its dark matter halo through processes like galaxy-galaxy merging, satellite accretion, and gas retention. Globular cluster formation is known to coincide with strong star formation events in the early Universe. To develop an accurate model of galaxy formation, the relationship between such systems and their hosting dark matter halos must be understood. Employing weak gravitational lensing galaxy mass analysis, we have discovered that the number of globular clusters in a given galaxy is directly proportional to its total dark matter halo mass. This result holds in both dwarf and giant ellipticals, spirals and in all types of galaxy environments. I will present these observations and initiate a discussion on the implications for scenarios of globular cluster system formation and evolution.

Based on observations with the Advanced Camera for Surveys (ACS), I will present accurate relative ages for a sample of 64 Galactic globular clusters. This Hubble Space Telescope (HST) Treasury program has been designed to provide a new large, deep and homogeneous photometric database. Relative ages have been obtained using a main sequence fitting procedure between clusters in the sample. Relative ages are determined with an accuracy from 2% to 7%. It has been proved that derived ages are independent of the assumed theoretical models. The existence of two well defined Galactic globular cluster groups is found. A group of old globular clusters with an age dispersion of 6% and showing no age-metallicity relation, and, on the other hand, a younger group showing a clear age-metallicity relation similar to that found in the globular clusters associated to the Sagittarius dwarf galaxy. Roughly 1/3 of the clusters belong to the younger group. Considering these new results, it is very tempting to suggest a Milky Way's halo formation scenario in which two differentiated phases took place. A very fast collapse, where the old and coeval globular clusters where formed, followed by accretions of Milky Way's satellite galaxies.

I present the first results of a long term project devoted to the study of the evolution of the binary population in globular clusters. Using deep ACS@HST images of a sample of 13 globular clusters I estimated the fraction of binaries in the cores of these clusters. From a theoretical side, I developed a simplified analytical code which simulates the evolution of the properties of the binary population in a dynamically evolving globular cluster. The comparison between theory and observations allows to evaluate the efficiency of the various processes of binary formation and destruction in these stellar systems and their dependence on the main cluster structural and dynamical parameters.