Examinando por Autor "Mennickent, RE"

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    DISCOVERY OF A METAL-POOR FIELD GIANT WITH A GLOBULAR CLUSTER SECOND-GENERATION ABUNDANCE PATTERN
    (IOP PUBLISHING, 2016-12) Fernandez-Trincado, JG; Robin, AC; Moreno, E; Schiavon, RP; Perez, AEG; Vieira, K; Cunha, K; Zamora, O; Sneden, C; Souto, D; Carrera, R; Johnson, JA; Shetrone, M; Zasowski, G; Garcia-Hernandez, DA; Majewski, SR; Reyle, C; Blanco-Cuaresma, S; Martinez-Medina, LA; Perez-Villegas, A; Valenzuela, O; Pichardo, B; Meza, A; Meszaros, S; Sobeck, J; Geisler, D; Anders, F; Schultheis, M; Tang, B; Roman-Lopes, A; Mennickent, RE; Pan, K; Nitschelm, C; Allard, F
    We report on the detection, from observations obtained with the Apache Point Observatory Galactic Evolution Experiment spectroscopic survey, of a metal-poor ([Fe/H] = -1.3 dex) field giant star with an extreme Mg-Al abundance ratio ([Mg/Fe] = -0.31 dex; [Al/Fe] = 1.49 dex). Such low Mg/Al ratios are seen only among the second-generation population of globular clusters (GCs) and are not present among Galactic disk field stars. The light-element abundances of this star, 2M16011638-1201525, suggest that it could have been born in a GC. We explore several origin scenarios, studying the orbit of the star in particular to check the probability of its being kinematically related to known GCs. We performed simple orbital integrations assuming the estimated distance of 2M16011638-1201525 and the available six-dimensional phase-space coordinates of 63 GCs, looking for close encounters in the past with a minimum distance approach within the tidal radius of each cluster. We found a very low probability that 2M16011638-1201525 was ejected from most GCs; however, we note that the best progenitor candidate to host this star is GC omega Centauri (NGC 5139). Our dynamical investigation demonstrates that 2M16011638-1201525 reaches a distance vertical bar Z(max)vertical bar < 3 kpc from the Galactic plane and minimum and maximum approaches to the Galactic center of R-min < 0.62 kpc and R-max < 7.26 kpc in an eccentric (e similar to 0.53) and retrograde orbit. Since the extreme chemical anomaly of 2M16011638-1201525 has also been observed in halo field stars, this object could also be considered a halo contaminant, likely to have been ejected into the Milky Way disk from the halo. We conclude that 2M16011638-20152 is also kinematically consistent with the disk but chemically consistent with halo field stars.
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    Ítem
    New spectroscopic binary companions of giant stars and updated metallicity distribution for binary systems
    (EDP SCIENCES, 2016-09) Bluhm, P; Jones, MI; Vanzi, L; Soto, MG; Voss, J; Wittenmyer, RA; Drass, H; Jenkins, JS; Olivares, F; Mennickent, RE; Vuckovic, M; Rojo, P; Melo, CHF
    We report the discovery of 24 spectroscopic binary companions to giant stars. We fully constrain the orbital solution for 6 of these systems. We cannot unambiguously derive the orbital elements for the remaining stars because the phase coverage is incomplete. Of these stars, 6 present radial velocity trends that are compatible with long-period brown dwarf companions. The orbital solutions of the 24 binary systems indicate that these giant binary systems have a wide range in orbital periods, eccentricities, and companion masses. For the binaries with restricted orbital solutions, we find a range of orbital periods of between similar to 97-1600 days and eccentricities of between similar to 0.1-0.4. In addition, we studied the metallicity distribution of single and binary giant stars. We computed the metallicity of a total of 395 evolved stars, 59 of wich are in binary systems. We find a flat distribution for these binary stars and therefore conclude that stellar binary systems, and potentially brown dwarfs, have a different formation mechanism than planets. This result is confirmed by recent works showing that extrasolar planets orbiting giants are more frequent around metal-rich stars. Finally, we investigate the eccentricity as a function of the orbital period. We analyzed a total of 130 spectroscopic binaries, including those presented here and systems from the literature. We find that most of the binary stars with periods. 30 days have circular orbits, while at longer orbital periods we observe a wide spread in their eccentricities.