Examinando por Autor "Moroni, P.G.P."

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  • Miniatura
    Ítem
    On a New Theoretical Framework for RR Lyrae Stars. II. Mid-infrared Period-Luminosity-Metallicity Relations
    (Institute of Physics Publishing, 2017-06) Neeley, J.R.; Marengo, M.; Bono, G.; Braga, V.F.; Dall'ora, M.; Magurno, D.; Marconi, M.; Trueba, N.; Tognelli, E.; Moroni, P.G.P.; Beaton, R.L.; Freedman, W.L.; Madore, B.F.; Monson, A.J.; Scowcroft, V.; Seibert, M.; Stetson, P.B.
    We present new theoretical period-luminosity-metallicity (PLZ) relations for RR Lyræ stars (RRLs) at Spitzer and WISE wavelengths. The PLZ relations were derived using nonlinear, time-dependent convective hydrodynamical models for a broad range of metal abundances (Z = 0.0001-0.0198). In deriving the light curves, we tested two sets of atmospheric models and found no significant difference between the resulting mean magnitudes. We also compare our theoretical relations to empirical relations derived from RRLs in both the field and in the globular cluster M4. Our theoretical PLZ relations were combined with multi-wavelength observations to simultaneously fit the distance modulus, μ 0, and extinction, A V, of both the individual Galactic RRL and of the cluster M4. The results for the Galactic RRL are consistent with trigonometric parallax measurements from Gaia's first data release. For M4, we find a distance modulus of μ 0 = 11.257 ± 0.035 mag with A V = 1.45 ± 0.12 mag, which is consistent with measurements from other distance indicators. This analysis has shown that, when considering a sample covering a range of iron abundances, the metallicity spread introduces a dispersion in the PL relation on the order of 0.13 mag. However, if this metallicity component is accounted for in a PLZ relation, the dispersion is reduced to ∼0.02 mag at mid-infrared wavelengths.
  • Miniatura
    Ítem
    THE ARAUCARIA PROJECT: A STUDY OF THE CLASSICAL CEPHEID IN THE ECLIPSING BINARY SYSTEM OGLE LMC562.05.9009 IN THE LARGE MAGELLANIC CLOUD
    (IOP PUBLISHING, 2015-12) Gieren, W.; Pilecki, B.; Pietrzyński, G.; Graczyk, D.; Udalski, A.; Soszyński, I.; Thompson, I.B.; Moroni, P.G.P.; Smolec, R.; Konorski, P.; Górski, M.; Karczmarek, P.; Suchomska, K.; Taormina, M.; Gallenne, A.; Storm, J.; Bono, G.; Catelan, M.; Szymański, M.; Kozłowski, S.; Pietrukowicz, P.; Wyrzykowski, Ł.; Poleski, R.; Skowron, J.; Minniti, D.; Ulaczyk, K.; Mróz, P.; Pawlak, M.; Nardetto, N.
    We present a detailed study of the classical Cepheid in the double-lined, highly eccentric eclipsing binary system OGLE-LMC562.05.9009. The Cepheid is a fundamental mode pulsator with a period of 2.988 days. The orbital period of the system is 1550 days. Using spectroscopic data from three 4-8-m telescopes and photometry spanning 22 years, we were able to derive the dynamical masses and radii of both stars with exquisite accuracy. Both stars in the system are very similar in mass, radius, and color, but the companion is a stable, non-pulsating star. The Cepheid is slightly more massive and bigger (M-1 = 3.70 +/- 0.03 Me-circle dot R-1 = 28.6 +/- 0.2 R-circle dot) than its companion (M-2 = 3.60. +/- 0.03 M-circle dot, R-2 = 26.6 +/- 0.2 R-circle dot). Within the observational uncertainties both stars have the same effective temperature of 6030 +/- 150 K. Evolutionary tracks place both stars inside the classical Cepheid instability strip, but it is likely that future improved temperature estimates will move the stable giant companion just beyond the red edge of the instability strip. Within current observational and theoretical uncertainties, both stars fit on a 205 Myr isochrone arguing for their common age. From our model, we determine a value of the projection factor of p = 1.37 +/- 0.07 for the Cepheid in the OGLE-LMC562.05.9009 system. This is the second Cepheid for which we could measure its p-factor with high precision directly from the analysis of an eclipsing binary system, which represents an important contribution toward a better calibration of Baade-Wesselink methods of distance determination for Cepheids.
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    Ítem
    The Gaia -ESO Survey: Open clusters in Gaia -DR1: A way forward to stellar age calibration
    (EDP Sciences, 2018-04) Randich, S.; Tognelli, E.; Jackson, R.; Jeffries, R.D.; Degl'Innocenti, S.; Pancino, E.; Fiorentin, P.R.; Spagna, A.; Sacco, G.; Bragaglia, A.; Magrini, L.; Moroni, P.G.P.; Alfaro, E.; Franciosini, E.; Morbidelli, L.; Roccatagliata, V.; Bouy, H.; Bravi, L.; Jiménez-Esteban, F.M.; Jordi, C.; Zari, E.; Tautvaišiene, G.; Drazdauskas, A.; Mikolaitis, S.; Gilmore, G.; Feltzing, S.; Vallenari, A.; Bensby, T.; Koposov, S.; Korn, A.; Lanzafame, A.; Smiljanic, R.; Bayo, A.; Carraro, G.; Costado, M.T.; Heiter, U.; Hourihane, A.; Jofré, P.; Lewis, J.; Monaco, L.; Prisinzano, L.; Sbordone, L.; Sousa, S.G.; Worley, C.C.; Zaggia, S.
    Context. Determination and calibration of the ages of stars, which heavily rely on stellar evolutionary models, are very challenging, while representing a crucial aspect in many astrophysical areas. Aims. We describe the methodologies that, taking advantage of Gaia-DR1 and the Gaia-ESO Survey data, enable the comparison of observed open star cluster sequences with stellar evolutionary models. The final, long-term goal is the exploitation of open clusters as age calibrators. Methods. We perform a homogeneous analysis of eight open clusters using the Gaia-DR1 TGAS catalogue for bright members and information from the Gaia-ESO Survey for fainter stars. Cluster membership probabilities for the Gaia-ESO Survey targets are derived based on several spectroscopic tracers. The Gaia-ESO Survey also provides the cluster chemical composition. We obtain cluster parallaxes using two methods. The first one relies on the astrometric selection of a sample of bona fide members, while the other one fits the parallax distribution of a larger sample of TGAS sources. Ages and reddening values are recovered through a Bayesian analysis using the 2MASS magnitudes and three sets of standard models. Lithium depletion boundary (LDB) ages are also determined using literature observations and the same models employed for the Bayesian analysis. Results. For all but one cluster, parallaxes derived by us agree with those presented in Gaia Collaboration (2017, A&A, 601, A19), while a discrepancy is found for NGC 2516; we provide evidence supporting our own determination. Inferred cluster ages are robust against models and are generally consistent with literature values. Conclusions. The systematic parallax errors inherent in the Gaia DR1 data presently limit the precision of our results. Nevertheless, we have been able to place these eight clusters onto the same age scale for the first time, with good agreement between isochronal and LDB ages where there is overlap. Our approach appears promising and demonstrates the potential of combining Gaia and ground-based spectroscopic datasets. © ESO 2018.