Browsing by Author "Clementini, Gisella"

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    Confirmation of a New Metal-poor Globular Cluster in the Galactic Bulge
    (2018) Minniti, D.; Schlafly, E. F.; Palma, Tali; Claria, Juan J.; Hempel, Maren; Alonso-Garcia, Javier; Bica, Eduardo; Bonatto, Charles; Braga, Vittorio F.; Clementini, Gisella; Garofalo, Alessia; Gomez, Matias; Ivanov, Valentin D.; Lucas, Phill
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    Looking for building blocks of the Galactic halo: variable stars in the Fornax, Bootes I, Canes Venatici II dwarfs and in NGC 2419
    (2010) Greco, Claudia; Clementini, Gisella; Held, E. V.; Poretti, E.; Catelan, Márcio; Federici, L.; Maio, M.; Gullieuszik, M.; Ripepi, V.; Dall'Ora, M.; Di Fabrizio, L.; Kinemuchi, K.; Di Crescienzo, M.; Marconi, M.; Musella, I.; Pritzl, B.; Rest, A.; De Lee, N.; Smith, H.
    Λ cold-dark-matter hierarchical models of galaxy formation suggest that the halo of the Milky Way (MW) has been assembled, at least in part, through accretion of protogalactic fragments partially resembling the present-day dwarf spheroidal (dSph) satellites of the MW. Investigation of the stellar populations of the MW's globular clusters (GCs) and dSph companions can thus provide excellent tests to infer the dominant Galaxy-formation scenario, whether merger/accretion or cloud collapse. Pulsating variable stars offer a very powerful tool in this context, since variables of different types allow tracing the different stellar generations in a galaxy and to reconstruct the galaxy's star-formation history and assembly back to the first epochs of galaxy formation. In particular, the RR Lyrae stars, belonging to the old population (t > 10 Gyr), witnessed the epoch of halo formation, and thus hold a crucial role to identify the MW satellites that may have contributed to build up the Galactic halo. In the MW, most GCs with an RR Lyrae population sharply divide into two distinct groups (Oosterhoff types I and II) based on the mean periods and relative proportion of fundamental-mode (RRab) and first-overtone (RRc) RR Lyrae stars. On the other hand, the Galactic-halo field RR Lyrae stars show a dominance of Oosterhoff I properties. Here, we investigate the Oosterhoff properties of a number of different stellar systems, starting from relatively undisturbed dwarf galaxies (the Fornax dSph and its globular clusters), through distorted and tidally disrupting ones (the Bootes and Canes Venatici II dSphs), to possible final relics of the disruption process (the Galactic globular cluster NGC 2419). We are addressing the crucial question of whether the RR Lyrae pulsation properties in these systems conform to the Oosterhoff dichotomy characterizing the MW variables. If they do not, the Galaxy's halo cannot have been assembled by dSph-like protogalactic fragments resembling the present-day dSph companions of the MW. We have reduced and combined long time series from different telescopes, both ground- and space-based. Variable stars have been detected with image-subtraction techniques using the package isis2.1. Periods, amplitudes and Oosterhoff type for all variable stars, as well as color-magnitude diagrams of the stellar populations are discussed for each stellar cluster analyzed....
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    Looking for the Building Blocks of the Galactic Halo: Variable stars in the Fornax, Bootes I, Canes Venatici II Dwarfs and in NGC2419
    (2009) Greco, Claudia; Clementini, Gisella; Held, Enrico E.; Poretti, Ennio; Catelan, Márcio; Federici, Luciana; Gullieuszik, Marco; Maio, Marcella; Ripepi, Vincenzo; Dall'Ora, Massimo; di Fabrizio, Luca; Kinemuchi, Karen; di Criscienzo, Marcella; Marconi, Marcella; Musella, Ilaria; Rest, Armin; de Lee, Nathan; Pritzl, Barton J.; Smith, Horace
    Looking for the building blocks of the Galactic Halo we have investigated and compared the properties of the RR Lyrae stars in a number of different stellar systems inside and outside the Milky Way.
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    RR Lyrae Variables in Stellar Systems
    (2009) Smith, Horace A.; Catelan, Marcio; Clementini, Gisella
    The pioneering studies of RR Lyrae stars in globular clusters by Oosterhoff and by Sawyer Hogg in the 1930s and 1940s called attention to interesting systematic differences among RR Lyrae populations in different systems. When such studies were extended to the dwarf spheroidal companions of the Milky Way in the 1960s, it was found that the average properties of their RR Lyrae stars were often different from those that had previously been observed in globular clusters. Observations of RR Lyrae stars have now extended to the Andromeda Galaxy and other Local Group systems, with still greater variety being apparent. Our understanding of the reasons for these differences among the RR Lyrae populations in different systems is by no means complete, but properties of RR Lyrae stars within these different systems are tied to differing horizontal branch morphologies and also shed light upon scenarios for the formation of the Galaxy....
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    Variable stars in the fornax dsph galaxy. I. The globular cluster fornax
    (2007) Greco, Claudia; Clementini, Gisella; Catelan, Marcio; Held, Enrico V.; Poretti, Ennio; Gullieuszik, Marco; Maio, Marcella; Rest, Armin; De Lee, Nathan; Smith, Horace A.; Pritzl, Barton J.
    Variable stars have been identified for the first time in Fornax 4, the globular cluster located near the center of the Fornax dwarf spheroidal galaxy. By applying the image-subtraction technique to B and V time series photometry obtained with the MagIC camera of the 6.5m Magellan Clay telescope and with the wide field imager of the 4 m Blanco CTIO telescope, we detected 27 RR Lyrae stars (22 fundamental-mode, 3 first-overtone, and 2 double-mode pulsators) in a 2.4' x 2.4' area centered on Fornax 4. The average and minimum periods of the ab-type RR Lyrae stars, < Pab > = 0: 594 days and P(ab,min) = 0.5191 days, respectively, as well as the revised position of the cluster in the horizontal branch type-metallicity plane, all consistently point to an Oosterhoff-intermediate status for the cluster, unlike what is seen for the vast majority of Galactic globular clusters, but in agreement with previous indications for the other globular clusters in Fornax. The average apparent magnitude of the RR Lyrae stars located within 3000 from the cluster center is < V(RR)> = 21.43 +/- 0.03 mag (sigma = 0.10 mag, average of 12 stars), leading to a true distance modulus of mu(0) = 20.64 +/- 0.09 mag or mu(0) = 20.53 +/- 0.09 mag, depending on whether a low ([Fe/H] = -2.0) or a moderately high ([Fe/H] = -1: 5) metallicity is adopted.