Browsing by Author "D'Orazi, V."

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    Kinematics of a globular cluster with an extended profile: NGC 5694
    (2015) Bellazzini, M.; Mucciarelli, A.; Sollima, A.; Catelan, Márcio; Dalessandro, E.; Correnti, M.; D'Orazi, V.; Cortés, C .; Amigo, P.
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    NGC 5694: another extra-galactic globular cluster
    (2013) Mucciarelli, A.; Bellazzini, M.; Catelan, Márcio; Amigo, P.; Correnti, M.; Cortés, C.; Dalessandro, E.; D'Orazi, V.
    We discuss the chemical composition of six giant stars of the outer Halo globular cluster NGC 5694, through the analysis of UVES@FLAMES high-resolution spectra. The cluster has an average iron content [Fe/H]=-1.83±0.01, solar-scaled [alpha /Fe] ratios and a very low Ba abundance ([Ba/Fe]=-0.71±0.06). These anomalous abundance patterns are different from those observed in other Halo globular clusters but similar to those of the metal-poor stars in typical dwarf spheroidal galaxies. These findings suggest an extra-galactic origin for NGC 5694, likely from a dwarf spheroidal galaxy....
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    On the chemical abundances of miras in clusters : V1 in the metal-rich globular NGC 5927
    (2018) D'Orazi, V.; Magurno, D.; Bono, G.; Matsunaga, N.; Braga, V.F.; Elgueta, S.S.; Fukue, K.; Hamano, S.; Inno, L.; Zoccali, Manuela; Kobayash, N.
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    On the Use of Field RR Lyrae as Galactic Probes. II. A New ΔS Calibration to Estimate Their Metallicity*
    (2021) Crestani, J.; Fabrizio, M.; Braga, V. F.; Sneden, C.; Preston, G.; Ferraro, I.; Iannicola, G.; Bono, G.; Alves-Brito, A.; Nonino, M.; D'Orazi, V.; Inno, L.; Monelli, M.; Storm, J.; Altavilla, G.; Chaboyer, B.; Dall'Ora, M.; Fiorentino, G.; Gilligan, C.; Grebel, E. K.; Lala, H.; Lemasle, B.; Marengo, M.; Marinoni, S.; Marrese, P. M.; Martinez-Vazquez, C. E.; Matsunaga, N.; Mullen, J. P.; Neeley, J.; Prudil, Z.; da Silva, R.; Stetson, P. B.; Thevenin, F.; Valenti, E.; Walker, A.; Zoccali, M.
    We performed the largest and most homogeneous spectroscopic survey of field RR Lyraes (RRLs). We secured 6300 high-resolution (HR, R similar to 35,000) spectra for 143 RRLs (111 fundamental, RRab; 32 first-overtone, RRc). The atmospheric parameters were estimated by using the traditional approach and the iron abundances were measured by using an LTE line analysis. The resulting iron distribution shows a well-defined metal-rich tail approaching solar iron abundance. This suggests that field RRLs experienced a complex chemical enrichment in the early halo formation. We used these data to develop a new calibration of the Delta S method. This diagnostic, based on the equivalent widths of Ca ii K and three Balmer (H-delta,H-gamma,H-beta) lines, traces the metallicity of RRLs. For the first time, the new empirical calibration: (i) includes spectra collected over the entire pulsation cycle; (ii) includes RRc variables; (iii) relies on spectroscopic calibrators covering more than three dex in iron abundance; and (iv) provides independent calibrations based on one/two/three Balmer lines. The new calibrations were applied to a data set of both SEGUE-SDSS and degraded HR spectra totalling 6451 low-resolution (R similar to 2000) spectra for 5001 RRLs (3439 RRab, 1562 RRc). This resulted in an iron distribution with a median eta = -1.55 0.01 and sigma = 0.51 dex, in good agreement with literature values. We also found that RRc are 0.10 dex more metal-poor than RRab variables, and have a distribution with a smoother metal-poor tail. This finding supports theoretical prescriptions suggesting a steady decrease in the RRc number when moving from metal-poor to metal-rich stellar environments.
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    On the Use of Field RR Lyrae as Galactic Probes. III. The α-element Abundances*
    (2021) Crestani, J.; Braga, V. F.; Fabrizio, M.; Bono, G.; Sneden, C.; Preston, G.; Ferraro, I.; Iannicola, G.; Nonino, M.; Fiorentino, G.; Thevenin, F.; Lemasle, B.; Prudil, Z.; Alves-Brito, A.; Altavilla, G.; Chaboyer, B.; Dall'Ora, M.; D'Orazi, V.; Gilligan, C.; Grebel, E. K.; Koch-Hansen, A. J.; Lala, H.; Marengo, M.; Marinoni, S.; Marrese, P. M.; Martinez-Vazquez, C.; Matsunaga, N.; Monelli, M.; Mullen, J. P.; Neeley, J.; da Silva, R.; Stetson, P. B.; Salaris, M.; Storm, J.; Valenti, E.; Zoccali, M.
    We provide the largest and most homogeneous sample of alpha-element (Mg, Ca, Ti) and iron abundances for field RR Lyrae (RRLs; 162 variables) by using high-resolution spectra. The current measurements were complemented with similar abundances available in the literature for 46 field RRLs brought to our metallicity scale. We ended up with a sample of old (t >= 10 Gyr), low-mass stellar tracers (208 RRLs: 169 fundamental, 38 first overtone, and 1 mixed mode) covering 3 dex in iron abundance (-3.00 <= [Fe/H] <= 0.24). We found that field RRLs are similar to 0.3 dex more alpha poor than typical halo tracers in the metal-rich regime ([Fe/H] >= -1.2), while in the metal-poor regime ([Fe/H] <= -2.2) they seem to be on average similar to 0.1 dex more alpha enhanced. This is the first time that the depletion in alpha elements for solar iron abundances is detected on the basis of a large, homogeneous, and coeval sample of old stellar tracers. Interestingly, we also detected a close similarity in the [alpha/Fe] trend between alpha-poor, metal-rich RRLs and red giants (RGs) in the Sagittarius dwarf galaxy as well as between alpha-enhanced, metal-poor RRLs and RGs in ultrafaint dwarf galaxies. These results are supported by similar elemental abundances for 46 field horizontal branch stars. These stars share with RRLs the same evolutionary phase and the same progenitors. This evidence further supports the key role that old stellar tracers play in constraining the early chemical enrichment of the halo and, in particular, in investigating the impact that dwarf galaxies have had in the mass assembly of the Galaxy.