Browsing by Author "Poretti, E."

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    A large and homogeneous sample of SX Phe stars in the Fornax dwarf spheroidal galaxy .
    (2006) Poretti, E.; Dell'Arciprete, L.; Clementini, G.; Held, E. V.; Greco, C.; Gullieuszik, M.; Maio, M.; Rizzi, L.; Catelan , Marcio; Smith, H. A.; Pritzl, B.; De Lee, N.; Rest, A.
    We report on the detection of sixty-one SX Phe stars in the Fornax dwarf spheroidal galaxy using the Wide-Field Imager at the 2.2m ESO-MPI telescope. In spite of their extreme faintness (22.0...
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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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    The Fornax Project
    (2006) Clementini, G.; Greco, C.; Held, E. V.; Poretti, E.; Catelan, Marcio; Dell'Arciprete, L.; Gullieuszik, M.; Maio, M.; Rizzi, L.; Smith, H. A.; Pritzl, B. J.; Rest, A.; De Lee, N.
    The Fornax Project aims at mapping the classical instability strip of the Fornax dwarf spheroidal galaxy, from the faint Dwarf Cepheids (V ∼ 24-25 mag) to the bright Anomalous Cepheids (V ∼ 19 mag). To achieve this goal, deep B,V time-series photometry of the galaxy has been obtained with the Wide Field Imagers (WFIs) of the ESO 2.2 m and CTIO 4 m telescopes, and the Clay camera at the Magellan 6.5 m telescope. Preliminary results are presented on the Oosterhoff classification of the RR Lyrae stars identified in a northern portion of Fornax field and in three of its globular clusters....
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    Variable stars in Fornax dwarf spheroidal galaxy
    (2005) Greco, C.; Clementini, G.; Held, E. V.; Poretti, E.; Catelan, Marcio; Dell'Arciprete, L.; Gullieuszik, M.; Maio, M.; Rizzi, L.; Smith, H. A.; Pritzl, B. J.; Rest, A.; De Lee, N.
    We present the first results of a variable star search in the field and in the globular clusters of the Fornax dwarf spheroidal galaxy. Variable stars were identified using the Image Subtraction Technique (Alard 2000) on time-series data obtained with the ESO 2.2 m and the Magellan 6.5 m telescopes. The variable star sample includes RR Lyrae stars, Dwarf Cepheids and Anomalous Cepheids. The pulsation properties (namely: periods, light curves, period-amplitude relations and classification in Oosterhoff types) of Fornax variables from the present study are discussed in some detail....
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    Variable Stars in the Globular Clusters and in the Field of the Fornax dSph Galaxy
    (2009) Greco, C.; Clementini, G.; Held, E. V.; Poretti, E.; Catelan, Marcio; Dell'Arciprete, L.; Gullieuszik, M.; Maio, M.; Rizzi, L.; Smith, H. A.; Pritzl, B. J.; Rest, A.; de Lee, N.
    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 6.5 m 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'×2.4' area centered on Fornax 4. The average and minimum periods of the ab-type RR Lyrae stars, =0.594 days and Pab,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 30" from the cluster center is =21.43+/-0.03 mag (σ=0.10 mag, average of 12 stars), leading to a true distance modulus of μ0=20.64+/-0.09 mag or μ0=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.