The Rise of the AGB in the Galactic Halo: Mg Isotopic Ratios and High Precision Elemental Abundances in M71 Giants

Abstract

High-resolution (R ~ 100 000), high signal-to-noise spectra of M71 giants have been obtained with HIRES at the KeckI Telescope in order to measure their Mg isotopic ratios, as well as elemental abundances of C, N, O, Na, Mg, Al, Si, Ca, Ti, Ni, Zr and La. We demonstrate that M71 has two populations, the first having weak CN, normal O, Na, Mg, and Al, and a low ratio of 26Mg/Mg (~4%) consistent with models of galactic chemical evolution with no contribution from AGB stars. The Galactic halo could have been formed from the dissolution of globular clusters prior to their intermediate mass stars reaching the AGB. The second population has enhanced Na and Al accompanied by lower O and by higher 26Mg/Mg (~8%), consistent with models which do incorporate ejecta from AGB stars via normal stellar winds. All the M71 giants have identical [Fe/H], [Si/Fe], [Ca/Fe], [Ti/Fe] and [Ni/Fe] to within sigma = 0.04 dex (10%). We therefore infer that the timescale for formation of the first generation of stars we see today in this globular cluster must be sufficiently short to avoid a contribution from AGB stars, i.e. less than ~0.3Gyr. Furthermore, the Mg isotopic ratios in the second M71 population, combined with their elemental abundances for the light elements, demonstrate that the difference must be the result of adding in the ejecta of intermediate mass AGB stars. Finally we suggest that the low amplitude of the abundance variations of the light elements within M71 is due to a combination of its low mass and its relatively high Fe-metallicity.

ApJ, in press

References in corpus (11)

• Fast rotating massive stars and the origin of the abundance patterns in galactic globular clusters
• Basic physical parameters of a selected sample of evolved stars
• Stellar Models and Yields of Asymptotic Giant Branch Stars
• Precise radial velocities of giant stars. III. Spectroscopic stellar parameters
• Chemical similarities between Galactic bulge and local thick disk red giant stars
• 3D Hydrodynamical Simulations of Surface Convection in Red Giant Stars. Impact on spectral line formation and abundance analysis
• Both accurate and precise gf-values for FeII lines
• A large C+N+O abundance spread in giant stars of the globular cluster NGC 1851
• Chemical abundances in giants stars of the tidally disrupted globular cluster NGC 6712 from high-resolution infrared spectroscopy
• Another forbidden solar oxygen abundance: the [O I] 5577 A line
• The link between chemical anomalies along the red giant branch and the horizontal branch extension in globular clusters

Cited by in corpus (33)

• Intrinsic iron spread and a new metallicity scale for Globular Clusters
• Properties of stellar generations in Globular Clusters and relations with global parameters
• Chemical similarities between Galactic bulge and local thick disk red giants: O, Na, Mg, Al, Si, Ca and Ti
• The remarkable solar twin HIP 56948: a prime target in the quest for other Earths
• Evolution and nucleosynthesis of asymptotic giant branch stellar models of low metallicity
• Exploring Anticorrelations and Light Element Variations in Northern Globular Clusters Observed by the APOGEE Survey
• Calibrations of Atmospheric Parameters Obtained from the First Year of SDSS-III APOGEE Observations
• Deep Mixing in Evolved Stars: I. The Effect of Reaction Rate Revisions from C to Al
• The Pisa Stellar Evolution Data Base for low-mass stars
• Heavy-element yields and abundances of Asymptotic Giant Branch models with a Small Magellanic Cloud metallicity
• Oxygen abundances in low- and high-alpha field halo stars and the discovery of two field stars born in globular clusters
• High Precision Differential Abundance Measurements in Globular Clusters: Chemical Inhomogeneities in NGC 6752
• Analysis of old very metal rich stars in the solar neighbourhood
• Element abundances in the stars of the MILES spectral library: the Mg/Fe ratio
• New atmospheric parameters and spectral interpolator for the MILES cool stars
• The chemical composition of red giants in 47 Tucanae I: Fundamental parameters and chemical abundance patterns
• Magnesium Isotope Ratios in omega Centauri Red Giants
• FORS2/VLT survey of Milky Way globular clusters I. Description of the method for derivation of metal abundances in the optical and application to NGC 6528, NGC 6553, M 71, NGC 6558, NGC 6426 and Terzan 8
• The iron dispersion of the globular cluster M 2, revised
• Light-Element Abundances of Giant Stars in the Globular Cluster M71 (NGC 6838)
• First direct limit on the 334 keV resonance strength in the ${}^{22}$Ne(α,γ)${}^{26}$Mg reaction
• The Cosmic Evolution of Magnesium Isotopes
• The chemical composition of red giants in 47 Tucanae. II. Magnesium isotopes and pollution scenarios
• Nucleosynthetic yields of Z=$10^{-5}$ intermediate-mass stars
• Chemical analysis of eight giant stars of the globular cluster NGC 6366
• An investigation of the formation and line properties of MgH in 3D hydrodynamical model stellar atmospheres
• A formation timescale of the Galactic halo from Mg isotopes in dwarf stars
• Magnesium isotope ratios in Milky Way and dwarf galaxy stars
• The complex stellar system M 22: constraining the chemical enrichment from AGB stars using magnesium isotope ratios
• Chemical enrichment by collapsars as the origin of the unusually high [Ba/Fe] in a massive star cluster of the dwarf galaxy NGC 1569
• Magnesium Isotopic Detection in Cool Stars: Tracing Nucleosynthetic Signatures from MgH Features
• The first galactic stars and chemical enrichment in the halo
• Globular Cluster Abundances and What They Can Tell Us About Galaxy Formation