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        A formation timescale of the Galactic halo from Mg isotopes in dwarf stars

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        Carlos_et_al_A_formation_timescale_of_the_galactic_halo_Accepted_Manuscript.pdf (PDF, 911Kb)
        Author
        Carlos, Marilia
        Karakas, Amanda I.
        Cohen, Judith G.
        Kobayashi, Chiaki
        Melendez, Jorge
        Attention
        2299/20252
        Abstract
        We determine magnesium isotopic abundances of metal-poor dwarf stars from the galactic halo, to shed light on the onset of asymptotic giant branch (AGB) star nucleosynthesis in the galactic halo and constrain the timescale of its formation. We observed a sample of eight new halo K dwarfs in a metallicity range of -1.9 < [Fe/H] < -0.9 and 4200 < T eff(K) < 4950, using the HIRES spectrograph at the Keck Observatory (R ≈ 10 5 and 200 ≤ S/N ≤ 300). We obtain magnesium isotopic abundances by spectral synthesis on three MgH features and compare our results with galactic chemical evolution models. With the current sample, we almost double the number of metal-poor stars with Mg isotopes determined from the literature. The new data allow us to determine the metallicity when the 26Mg abundances start to become important, [Fe/H] ∼ -1.4 ± 0.1. The data with [Fe/H] > -1.4 are somewhat higher (1-3σ) than previous chemical evolution model predictions, indicating perhaps higher yields of the neutron-rich isotopes. Our results using only AGB star enrichment suggest a timescale for formation for the galactic halo of about 0.3 Gyr, but considering also supernova enrichment, the upper limit for the timescale formation is about 1.5 Gyr.
        Publication date
        2018-04-04
        Published in
        The Astrophysical Journal
        Published version
        https://doi.org/10.3847/1538-4357/aab36c
        Other links
        http://hdl.handle.net/2299/20252
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