Examinando por Autor "Schultheis, M"

Mostrando 1 - 2 de 2
  • Miniatura
    Ítem
    Chemical trends in the Galactic halo from APOGEE data
    (OXFORD UNIV PRESS, 2016-11) Fernandez-Alvar, E; Carigi, L; Prieto, CA; Hayden, MR; Beers, TC; Fernandez-Trincado, JG; Meza, A; Schultheis, M; Santiago, BX; Queiroz, AB; Anders, F; da Costa, LN; Chiappini, C
    The galaxy formation process in the A cold dark matter scenario can be constrained from the analysis of stars in the Milky Way's halo system. We examine the variation of chemical abundances in distant halo stars observed by the Apache Point Observatory Galactic Evolution Experiment ( APOGEE), as a function of distance from the Galactic Centre ( r) and iron abundance ([M/H]), in the range 5 less than or similar to r less than or similar to 30 kpc and - 2.5<[M/H] < 0.0. We perform a statistical analysis of the abundance ratios derived by the APOGEE pipeline ( ASPCAP) and distances calculated by several approaches. Our analysis reveals signatures of a different chemical enrichment between the inner and outer regions of the halo, with a transition at about 15 kpc. The derived metallicity distribution function exhibits two peaks, at [M/H]similar to -1.5 and similar to -2.1, consistent with previously reported halo metallicity distributions. We obtain a difference of similar to 0.1 dex for alpha- element-to-iron ratios for stars at r > 15 kpc and [M/H] > - 1.1 (larger in the case of O, Mg, and S) with respect to the nearest halo stars. This result confirms previous claims for low-alpha stars found at larger distances. Chemical differences in elements with other nucleosynthetic origins (Ni, K, Na, and Al) are also detected. C and N do not provide reliable information about the interstellar medium from which stars formed because our sample comprises red giant branch and asymptotic giant branch stars and can experience mixing of material to their surfaces.
  • Miniatura
    Ítem
    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.