Browsing by Author "Ferraro, F. R."

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    NEW DENSITY PROFILE AND STRUCTURAL PARAMETERS OF THE COMPLEX STELLAR SYSTEM TERZAN 5
    (2010) Lanzoni, B.; Ferraro, F. R.; Dalessandro, E.; Mucciarelli, A.; Beccari, G.; Miocchi, P.; Bellazzini, M.; Rich, R. M.; Origlia, L.; Valenti, E.; Rood, R. T.; Ransom, S. M.
    Terzan 5 is a globular cluster-like stellar system in the Galactic bulge which has been recently found to harbor two stellar populations with different iron content and probably different ages. This discovery suggests that Terzan 5 may be the relic of a primordial building block that contributed to the formation of the Galactic bulge. Here we present a re-determination of the structural parameters (center of gravity, density and surface brightness profiles, total luminosity, and mass) of Terzan 5, as obtained from the combination of high-resolution (ESO-MAD and Hubble Space Telescope ACS-WFC) and wide-field (ESO-WFI) observations. We find that Terzan 5 is significantly less concentrated and more massive than previously thought. Still it has the largest collision rate of any stellar aggregate in the Galaxy. We discuss the impact of these findings on the exceptional population of millisecond pulsars harbored in this stellar system.
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    The cluster Terzan 5 as a remnant of a primordial building block of the Galactic bulge
    (2009) Ferraro, F. R.; Dalessandro, E.; Mucciarelli, A.; Beccari, G.; Rich, R. M.; Origlia, L.; Lanzoni, B.; Rood, R. T.; Valenti, E.; Bellazzini, M.; Ransom, S. M.; Cocozza, G.
    Globular star clusters are compact and massive stellar systems old enough to have witnessed the entire history of our Galaxy, the Milky Way. Although recent results(1-3) suggest that their formation may have been more complex than previously thought, they still are the best approximation to a stellar population formed over a relatively short timescale (less than 1 Gyr) and with virtually no dispersion in the iron content. Indeed, only one cluster-like system (omega Centauri) in the Galactic halo is known to have multiple stellar populations with a significant spread in iron abundance and age(4,5). Similar findings in the Galactic bulge have been hampered by the obscuration arising from thick and varying layers of interstellar dust. Here we report that Terzan 5, a globular-cluster-like system in the Galactic bulge, has two stellar populations with different iron contents and ages. Terzan 5 could be the surviving remnant of one of the primordial building blocks that are thought to merge and form galaxy bulges.
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    The Trimodal Horizontal Branch of M75 (NGC 6864)
    (2002) Catelan, Marcio; Borissova, J.; Ferraro, F. R.; Corwin, T. M.; Smith, H. A.
    Deep UBVI photometry for a large field covering the distant globular cluster M75 (NGC 6864) is presented. We confirm a previous suggestion (Catelan et al. 1998) that M75 possesses a bimodal horizontal branch (HB) bearing striking resemblance to the well-know case of NGC 1851. In addition, we detect a third, smaller grouping of stars may correspond to the upper part of a very extended, though thinly populated, blue tail. Thus M75 appears to have a trimodal HB. The presence of the "Grundahl jump" is verified using the broadband U filter.