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

@article{Melndez2007MagnesiumII,
  title={Magnesium Isotopes in Metal-poor Dwarfs: The Rise of AGB Stars and the Formation Timescale of the Galactic Halo},
  author={Jorge Mel{\'e}ndez and Judith G. Cohen},
  journal={The Astrophysical Journal Letters},
  year={2007},
  volume={659},
  pages={L25 - L28}
}
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… 

Figures and Tables from this paper

THE RISE OF THE AGB IN THE GALACTIC HALO: Mg ISOTOPIC RATIOS AND HIGH PRECISION ELEMENTAL ABUNDANCES IN M71 GIANTS
High-resolution (R≈ 100,000), high signal-to-noise spectra of M71 giants have been obtained with High Resolution Echelle Spectrometer at the Keck I telescope in order to measure their Mg isotopic
MAGNESIUM ISOTOPE RATIOS IN ω CENTAURI RED GIANTS
We have used the high-resolution observations obtained at the Anglo-Australian Telescope with Ultra-High Resolution Facility (R ∼ 100,000) and at Gemini-S with b-HROS (R ∼ 150,000) to determine
Light element abundances in carbon-enhanced metal-poor stars
We model the evolution of the abundances of light elements in carbon-enhanced metal-poor (CEMP) stars, under the assumption that such stars are formed by mass transfer in a binary system. We have
The evolution of isotope ratios in the Milky Way Galaxy
Isotope ratios have opened a new window into the study of the details of stellar evolution, supernovae, and galactic chemical evolution. We present the evolution of the isotope ratios of elemental
The cosmic evolution of magnesium isotopes
The abundance of magnesium in the interstellar medium is a powerful probe of star formation processes over cosmological time-scales. Magnesium has three stable isotopes, ^24Mg, ^25Mg, and ^26Mg,
EVOLUTION AND NUCLEOSYNTHESIS OF ASYMPTOTIC GIANT BRANCH STELLAR MODELS OF LOW METALLICITY
We present stellar evolutionary tracks and nucleosynthetic predictions for a grid of stellar models of low- and intermediate-mass asymptotic giant branch (AGB) stars at Z = 0.001 ([Fe/H] =−1.2). The
Heavy Element Abundances in Giant Stars of the Globular Clusters M4 and M5
We present a comprehensive abundance analysis of 27 heavy elements in bright giant stars of the globular clusters M4 and M5 based on high-resolution, high signal-to-noise ratio spectra obtained with
NUCLEOSYNTHESIS PREDICTIONS FOR INTERMEDIATE-MASS ASYMPTOTIC GIANT BRANCH STARS: COMPARISON TO OBSERVATIONS OF TYPE I PLANETARY NEBULAE
Type I planetary nebulae (PNe) have high He/H and N/O ratios and are thought to be descendants of stars with initial masses of ∼3–8 M☉. These characteristics indicate that the progenitor stars
Nucleosynthetic yields of Z = 10−5 intermediate-mass stars
Context. Observed abundances of extremely metal-poor stars in the Galactic halo hold clues for understanding the ancient universe. Interpreting these clues requires theoretical stellar models in a
The Origin of Elements from Carbon to Uranium
To reach a deeper understanding of the origin of elements in the periodic table, we construct Galactic chemical evolution (GCE) models for all stable elements from C (A = 12) to U (A = 238) from
...
...

References

SHOWING 1-10 OF 34 REFERENCES
The Isotopic Abundances of Magnesium in Stars
Isotopic abundance ratios 24Mg : 25Mg : 26Mg are derived for 20 stars from high-resolution spectra of the MgH A-X 0-0 band at 5140 Å. With the exception of the weak G-band giant HR 1299, the stars
Magnesium Isotopic Abundance Ratios in Cool Stars
From high-resolution spectra of 61 cool dwarfs and giants, Mg isotopic abundance ratios 24Mg : 25Mg : 26Mg are derived from spectral synthesis of the MgH A-X lines near 5140 Å. Our sample spans the
The origin of nitrogen - Implications of recent measurements of N/O in Galactic metal-poor halo stars
Recent new high-precision abundance data for Galactic halo stars suggest important primary nitrogen production in very metal-poor massive stars. Here, we compute a new model for the chemical
The Chemical Evolution of Magnesium Isotopic Abundances in the Solar Neighbourhood
Abstract The abundance of the neutron-rich magnesium isotopes observed in metal-poor stars is explained quantitatively with a chemical evolution model of the local Galaxy that considers — for the
Permitted Oxygen Abundances and the Temperature Scale of Metal-poor Turnoff Stars
We use high-quality VLT/UVES published data of the permitted O I triplet and Fe II lines to determine oxygen and iron abundances in unevolved (dwarfs, turnoff, subgiants) metal-poor halo stars. The
Isotopic abundances of magnesium in five G and K dwarfs
High-resolution low-noise Reticon observations of MgH lines in the spectra of ..mu.. Cas, epsilon Eri, 61 Cyg A and B, and Gmb 1830 have been analyzed by spectrum synthesis. The mixtures of the
Production of Aluminium and the Heavy Magnesium Isotopes in Asymptotic Giant Branch Stars
Abstract We investigate the production of aluminium and magnesium in asymptotic giant branch models covering a wide range in mass and composition. We evolve models from the pre-main sequence, through
The Fine-Structure Constant as a Probe of Chemical Evolution and Asymptotic Giant Branch Nucleosynthesis in Damped Lyα Systems
Evidence from a large sample of quasar absorption-line spectra in damped Lyα systems has suggested a possible time variation of the fine-structure constant, α. The most statistically significant
Keck NIRSPEC Infrared OH Lines: Oxygen Abundances in Metal-poor Stars down to [Fe/H] = –2.9
Infrared OH lines at 1.5-1.7 μm in the H band were obtained with the NIRSPEC high-resolution spectrograph at the 10 m Keck Telescope for a sample of seven metal-poor stars. Detailed analyses have
Elemental abundance trends in the Galactic thin and thick disks as traced by nearby F and G dwarf stars
Based on spectra from F and G dwarf stars, we present elementalabundance trends in the Galactic thin and thick disks in the metallicityregime -0.8< [Fe/H < +0.4. Our findings can besummarized as
...
...