Examinando por Autor "Zamora, O."
Mostrando 1 - 5 de 5
Resultados por página
Opciones de ordenación
Ítem A Chemical and Kinematical Analysis of the Intermediate-age Open Cluster IC 166 from APOGEE and Gaia DR2(Institute of Physics Publishing, 2018-09) Schiappacasse-Ulloa, J.; Tang, B.; Fernández-Trincado, J.G.; Zamora, O.; Geisler, D.; Frinchaboy, P.; Schultheis, M.; Dell'Agli, F.; Villanova, S.; Masseron, T.; Mészáros, S.; Souto, D.; Hasselquist, S.; Cunha, K.; Smith, V.V.; García-Hernández, D.A.; Vieira, K.; Robin, A.C.; Minniti, D.; Zasowski, G.; Moreno, E.; Pérez-Villegas, A.; Lane, R.R.; Ivans, I.I.; Pan, K.; Nitschelm, C.; Santana, F.A.; Carrera, R.; Roman-Lopes, A.IC 166 is an intermediate-age open cluster (OC) (∼1 Gyr) that lies in the transition zone of the metallicity gradient in the outer disk. Its location, combined with our very limited knowledge of its salient features, make it an interesting object of study. We present the first high-resolution spectroscopic and precise kinematical analysis of IC 166, which lies in the outer disk with R GC ∼ 12.7 kpc. High-resolution H-band spectra were analyzed using observations from the SDSS-IV Apache Point Observatory Galactic Evolution Experiment survey. We made use of the Brussels Automatic Stellar Parameter code to provide chemical abundances based on a line-by-line approach for up to eight chemical elements (Mg, Si, Ca, Ti, Al, K, Mn, and Fe). The α-element (Mg, Si, Ca, and whenever available Ti) abundances, and their trends with Fe abundances have been analyzed for a total of 13 high-likelihood cluster members. No significant abundance scatter was found in any of the chemical species studied. Combining the positional, heliocentric distance, and kinematic information, we derive, for the first time, the probable orbit of IC 166 within a Galactic model including a rotating boxy bar, and found that it is likely that IC 166 formed in the Galactic disk, supporting its nature as an unremarkable Galactic OC with an orbit bound to the Galactic plane. © 2018. The American Astronomical Society.Ítem Cool stars in the Galactic center as seen by APOGEE: M giants, AGB stars, and supergiant stars and candidates(EDP Sciences, 2020-10) Schultheis, M.; Rojas-Arriagada, A.; Cunha, K.; Zoccali, M.; Chiappini, C.; Zasowski, G.; Queiroz, A.B.A.; Minniti, D.; Fritz, T.; Garciá-Hernández, D.A.; Nitschelm, C.; Zamora, O.The Galactic center region, including the nuclear disk, has until recently been largely avoided in chemical census studies because of extreme extinction and stellar crowding. Large, near-IR spectroscopic surveys, such as the Apache Point Observatory Galactic Evolution Experiment (APOGEE), allow the measurement of metallicities in the inner region of our Galaxy. Making use of the latest APOGEE data release (DR16), we are able for the first time to study cool Asymptotic Giant branch (AGB) stars and supergiants in this region. The stellar parameters of five known AGB stars and one supergiant star (VR 5-7) show that their location is well above the tip of the red giant branch. We studied metallicities of 157 M giants situated within 150 pc of the Galactic center from observations obtained by the APOGEE survey with reliable stellar parameters from the APOGEE pipeline making use of the cool star grid down to 3200 K. Distances, interstellar extinction values, and radial velocities were checked to confirm that these stars are indeed situated in the Galactic center region. We detect a clear bimodal structure in the metallicity distribution function, with a dominant metal-rich peak of [Fe/H] ∼+0.3 dex and a metal-poor peak around {Fe/H] = -0.5 dex, which is 0.2 dex poorer than Baade's Window. The α-elements Mg, Si, Ca, and O show a similar trend to the Galactic bulge. The metal-poor component is enhanced in the α-elements, suggesting that this population could be associated with the classical bulge and a fast formation scenario. We find a clear signature of a rotating nuclear stellar disk and a significant fraction of high-velocity stars with vgal > 300 km s-1; the metal-rich stars show a much higher rotation velocity (∼200 km s-1) with respect to the metal-poor stars (∼140 km s-1). The chemical abundances as well as the metallicity distribution function suggest that the nuclear stellar disk and the nuclear star cluster show distinct chemical signatures and might be formed differently. © M. Schultheis et al. 2020.Ítem Disentangling the Galactic Halo with APOGEE. I. Chemical and Kinematical Investigation of Distinct Metal-poor Populations(Institute of Physics Publishing, 2018) Hayes, C.R.; Majewski, S.R.; Shetrone, M.; Fernández-Alvar, E.; Prieto, C.A.; Schuster, W.J.; Carigi, L.; Cunha, K.; Smith, V.V.; Sobeck, J.; Almeida, A.; Beers, T.C.; Carrera, R.; Fernández-Trincado, J.G.; García-Hernández, D.A.; Geisler, D.; Lane, R.R.; Lucatello, S.; Matthews, A.M.; Minniti, D.; Nitschelm, C.; Tang, B.; Tissera, P.B.; Zamora, O.We find two chemically distinct populations separated relatively cleanly in the [Fe/H]-[Mg/Fe] plane, but also distinguished in other chemical planes, among metal-poor stars (primarily with metallicities [Fe H] < -0.9) observed by the Apache Point Observatory Galactic Evolution Experiment (APOGEE) and analyzed for Data Release 13 (DR13) of the Sloan Digital Sky Survey. These two stellar populations show the most significant differences in their [X/Fe] ratios for the α-elements, C+N, Al, and Ni. In addition to these populations having differing chemistry, the low metallicity high-Mg population (which we denote "the HMg population") exhibits a significant net Galactic rotation, whereas the low-Mg population (or "the LMg population") has halo-like kinematics with little to no net rotation. Based on its properties, the origin of the LMg population is likely an accreted population of stars. The HMg population shows chemistry (and to an extent kinematics) similar to the thick disk, and is likely associated with in situ formation. The distinction between the LMg and HMg populations mimics the differences between the populations of low- and high-α halo stars found in previous studies, suggesting that these are samples of the same two populations.Ítem Disentangling the Galactic Halo with APOGEE. II. Chemical and Star Formation Histories for the Two Distinct Populations(Institute of Physics Publishing, 2018) Fernández-Alvar, E.; Carigi, L.; Schuster, W.J.; Hayes, C.R.; Ávila-Vergara, N.; Majewski, S.R.; Allende Prieto, C.; Beers, T.C.; Sánchez, S.F.; Zamora, O.; García-Hernández, D.A.; Tang, B.; Fernández-Trincado, J.G.; Tissera, P.; Geisler, D.; Villanova, S.The formation processes that led to the current Galactic stellar halo are still under debate. Previous studies have provided evidence for different stellar populations in terms of elemental abundances and kinematics, pointing to different chemical and star formation histories (SFHs). In the present work, we explore, over a broader range in metallicity (-2.2 < [Fe H] < +0.5), the two stellar populations detected in the first paper of this series from metal-poor stars in DR13 of the Apache Point Observatory Galactic Evolution Experiment (APOGEE). We aim to infer signatures of the initial mass function (IMF) and the SFH from the two α-to-iron versus iron abundance chemical trends for the most APOGEE-reliable α-elements (O, Mg, Si, and Ca). Using simple chemical-evolution models, we infer the upper mass limit (M up) for the IMF and the star formation rate, and its duration for each population. Compared with the low-α population, we obtain a more intense and longer-lived SFH, and a top-heavier IMF for the high-α population.Ítem Massive stars in the SDSS-IV/APOGEE SURVEY. I. OB stars(Institute of Physics Publishing, 2018-03) Roman-Lopes, A.; Román-Zúñiga, C.; Tapia, M.; Chojnowski, D.; Gómez Maqueo Chew, Y.; García-Hernández, D.A.; Borissova, J.; Minniti, D.; Covey, K.R.; Longa-Peña, P.; Fernandez-Trincado, J.G.; Zamora, O.; Nitschelm, C.In this work, we make use of DR14 APOGEE spectroscopic data to study a sample of 92 known OB stars. We developed a near-infrared semi-empirical spectral classification method that was successfully used in case of four new exemplars, previously classified as later B-type stars. Our results agree well with those determined independently from ECHELLE optical spectra, being in line with the spectral types derived from the "canonical" MK blue optical system. This confirms that the APOGEE spectrograph can also be used as a powerful tool in surveys aiming to unveil and study a large number of moderately and highly obscured OB stars still hidden in the Galaxy. © 2018. The American Astronomical Society. All rights reserved.