Magnesium Isotopes in Metal-poor Dwarfs: The Rise of AGB Stars and the Formation Timescale of the Galactic Halo
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).
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.- Publication:
-
The Astrophysical Journal
- Pub Date:
- April 2007
- DOI:
- 10.1086/516735
- arXiv:
- arXiv:astro-ph/0702655
- Bibcode:
- 2007ApJ...659L..25M
- Keywords:
-
- Galaxy: Halo;
- Stars: Abundances;
- Stars: AGB and Post-AGB;
- Stars: Atmospheres;
- Stars: Population II;
- Astrophysics
- E-Print:
- ApJ Letters, in press