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Magnesium Isotopes in Metal-poor Dwarfs: The Rise of AGB Stars and the Formation Timescale of the Galactic Halo*

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Published 2007 March 9 © 2007. The American Astronomical Society. All rights reserved. Printed in U.S.A.
, , Citation Jorge Meléndez and Judith G. Cohen 2007 ApJ 659 L25 DOI 10.1086/516735

1538-4357/659/1/L25

Abstract

We have determined magnesium isotopic ratios (25, 26Mg/Mg) in metal-poor (-2.6 ≤ [Fe/H] ≤ -1.3) halo dwarfs employing high signal-to-noise ratio (S/N = 90-280), high spectral resolution (R = 105) Keck High Resolution Echelle Spectrometer (HIRES) spectra. Unlike previous claims of an important contribution from intermediate-mass asymptotic giant branch (AGB) stars at low metallicities, we find that the rise of the AGB contribution in the Galactic halo did not occur until intermediate metallicities ([Fe/H] ≳ -1.5).

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Footnotes

  • The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration.

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10.1086/516735