Examinando por Autor "Neeley, J.R."
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Ítem 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.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.