Examinando por Autor "Mateo, M."

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    Chemical Compositions of Field and Globular Cluster RR Lyrae Stars. I. NGC 3201
    (Institute of Physics Publishing, 2018-09) Magurno, D.; Sneden, C.; Braga, V.F.; Bono, G.; Mateo, M.; Persson, S.E.; Dall'Ora, M.; Marengo, M.; Monelli, M.; Neeley, J.R.
    We present a detailed spectroscopic analysis of horizontal branch stars in the globular cluster NGC 3201. We collected optical (4580-5330), high-resolution (∼34,000), high signal-to-noise ratio (∼200) spectra for 11 RR Lyrae stars and one red horizontal branch star with the multifiber spectrograph M2FS with the 6.5 m Magellan telescope at the Las Campanas Observatory. From measured equivalent widths, we derived atmospheric parameters and abundance ratios for (Mg, Ca, and Ti), iron-peak (Sc, Cr, Ni, and Zn), and s-process (Y) elements. We found that NGC 3201 is a homogeneous, monometallic ([Fe/H] = -1.47 ± 0.04), enhanced ([/Fe] = 0.37 ± 0.04) cluster. The relative abundances of the iron-peak and s-process elements were found to be consistent with solar values. In comparison with other large stellar samples, NGC 3201 RR Lyraes have similar chemical enrichment histories as do those of other old (t ≥ 10 Gyr) Halo components (globular clusters; red giants; blue and red horizontal branch stars; and RR Lyraes). We also provided a new average radial velocity estimate for NGC 3201 by using a template velocity curve to overcome the limit of single-epoch measurements of variable stars: Vrad = 494 ± 2 km s-1 (σ = 8 km s-1). © 2018. The American Astronomical Society. All rights reserved.
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    On a New Method to Estimate the Distance, Reddening, and Metallicity of RR Lyrae Stars Using Optical/Near-infrared (B, V, I, J, H, K ) Mean Magnitudes: ω Centauri as a First Test Case
    (Astrophysical Journal, 2019-01-10) Bono, G.; Iannicola, G.; Braga, V. F.; Ferraro, I.; Stetson, P. B.; Magurno, D.; Matsunaga, N.; Beaton, R. L.; Buonanno, R.; Chaboyer, B.; Dall’Ora, M.; Fabrizio, M.; Fiorentino, G.; Freedman, W. L.; Gilligan, C. K.; Madore, B. F.; Marconi, M.; Marengo, M.; Marinoni, S.; Marrese, P. M.; Martinez-Vazquez, C. E.; Mateo, M.; Monelli, M.; Neeley, J. R.; Nonino, M.; Sneden, C.; Thevenin, F.; Valenti, E.; Walker, A. R.
    We developed a new approach to provide accurate estimates of the metal content, reddening, and true distance modulus of RR Lyrae stars (RRLs). The method is based on homogeneous optical (BVI) and near-infrared (JHK) mean magnitudes and on predicted period-luminosity-metallicity relations (IJHK) and absolute mean magnitude-metallicity relations (BV). We obtained solutions for three different RRL samples in ω Cen: first overtone (RRc, 90), fundamental (RRab, 80), and global (RRc+RRab) in which the period of first overtones were fundamentalized. The metallicity distribution shows a well defined peak at [Fe/H]∼-1.98 and a standard deviation of σ = 0.54 dex. The spread is, as expected, metal-poor ([Fe/H] ≤ -2.3) objects. The current metallicity distribution is ∼0.3 dex more metal-poor than similar estimates for RRLs available in the literature. The difference vanishes if the true distance modulus we estimated is offset by -0.06/-0.07 mag in true distance modulus. We also found a cluster true distance modulus of μ = 13.720 ±0.002 ±0.030 mag, where the former error is the error on the mean and the latter is the standard deviation. Moreover, we found a cluster reddening of E(B - V) = 0.132 ±0.002 ±0.028 mag and spatial variations of the order of a few arcmin across the body of the cluster. Both the true distance modulus and the reddening are slightly larger than similar estimates available in the literature, but the difference is within 1σ. The metallicity dependence of distance diagnostics agrees with theory and observations, but firm constraints require accurate and homogeneous spectroscopic measurements.