Deep Mixing and Metallicity: Carbon Depletion in Globular Cluster Giants

Abstract

We present the results of an observational study of the efficiency of deep mixing in globular cluster red giants as a function of stellar metallicity. We determine [C/Fe] abundances based on low-resolution spectra taken with the Kast spectrograph on the 3m Shane telescope at Lick Observatory. Spectra centered on the 4300 Angstrom CH absorption band were taken for 42 bright red giants in 11 Galactic globular clusters ranging in metallicity from M92 ([Fe/H]=-2.29) to NGC 6712 ([Fe/H]=-1.01). Carbon abundances were derived by comparing values of the CH bandstrength index S2(CH) measured from the data with values measured from a large grid of SSG synthetic spectra. Present-day abundances are combined with theoretical calculations of the time since the onset of mixing, which is also a function of stellar metallicity, to calculate the carbon depletion rate across our metallicity range. We find that the carbon depletion rate is twice as high at a metallicity of [Fe/H]=-2.3 than at [Fe/H]=-1.3, which is a result qualitatively predicted by some theoretical explanations of the deep mixing process.

arXiv comment10 pages including 11 figures, emulateapj format, accepted by AJ

References in corpus (14)

• Thermohaline mixing: A physical mechanism governing the photospheric composition of low-mass giants
• A consistent explanation for ${}^{12}$C/${}^{13}$C, ${}^7$Li, and ${}^3$He anomalies in red giant stars
• Rotational mixing in low-mass stars II. Self-consistent models of Pop II RGB stars
• A critical investigation on the discrepancy between the observational and theoretical Red Giant luminosity function "Bump"
• Comparison between predicted and empirical DV(Bump -HB) in Galactic Globular Clusters
• Abundance Anomalies and Rotational Evolution of Low Mass Red Giants: A Maximal Mixing Approach
• Aluminum Abundances, Deep Mixing and the Blue-Tail Second-Parameter Effect in the Globular Clusters M 3 and M 13
• The Red Giant Branch Luminosity Function Bump
• The shape of the Red Giant Branch Bump as a diagnostic of partial mixing processes in low-mass stars
• Calibration of the CH and CN Variations Among Main Sequence Stars in M71 and in M13
• CN Bimodality at Low Metallicity: The Globular Cluster M53
• 3He-Driven Mixing in Low-Mass Red Giants: Convective Instability in Radiative and Adiabatic Limits
• An Improved Bandstrength Index for the CH G Band of Globular Cluster Giants
• CN and CH Band Strengths of Bright Giants in M3

Cited by in corpus (50)

• The Dawes Review 2: Nucleosynthesis and stellar yields of low and intermediate-mass single stars
• What is a globular cluster? An observational perspective
• Red giant masses and ages derived from carbon and nitrogen abundances
• Chemical tagging with APOGEE: Discovery of a large population of N-rich stars in the inner Galaxy
• Carbon, nitrogen and $\alpha$-element abundances determine the formation sequence of the Galactic thick and thin disks
• Exploring Anticorrelations and Light Element Variations in Northern Globular Clusters Observed by the APOGEE Survey
• The SUMO project I. A survey of multiple populations in globular clusters
• Light-element Abundance Variations in the Milky Way Halo
• Numerical Simulations of Thermohaline Convection: Implications for Extra-Mixing in Low-Mass RGB Stars
• The extremely low-metallicity tail of the Sculptor dwarf spheroidal galaxy
• Chemical tagging in the SDSS-III/APOGEE survey: new identifications of halo stars with globular cluster origins
• Detailed abundance analysis from integrated high-dispersion spectroscopy: Globular clusters in the Fornax Dwarf Spheroidal
• Constraining stellar population models - I. Age, metallicity, and abundance pattern compilation for Galactic globular clusters
• Carbon in Red Giants in Globular Clusters and Dwarf Spheroidal Galaxies
• Helium and Multiple Populations in the Massive Globular Cluster NGC6266 (M62)
• Lithium-Rich Field Giants in the Sloan Digital Sky Survey
• The depletion of carbon by extra mixing in metal-poor giants
• A large and pristine sample of standard candles across the Milky Way: ~100,000 red clump stars with 3% contamination
• The Gaia-ESO survey: Calibrating a relationship between Age and the [C/N] abundance ratio with open clusters
• The Role of Thermohaline Mixing in Intermediate- and Low-Metallicity Globular Clusters
• NGC 6535: the lowest mass Milky Way globular cluster with a Na-O anti-correlation? Cluster mass and age in the multiple population context
• Ages and Masses of 0.64 million Red Giant Branch stars from the LAMOST Galactic Spectroscopic Survey
• A Survey of CN and CH Variations in Galactic Globular Clusters from SDSS Spectroscopy
• Constraints on the Distance Moduli, Helium and Metal Abundances, and Ages of Globular Clusters from their RR Lyrae and Non-Variable Horizontal-Branch Stars. I. M3, M15, and M92
• Thermohaline Mixing and its Role in the Evolution of Carbon and Nitrogen Abundances in Globular Cluster Red Giants: The Test Case of Messier 3
• Exploring the stellar age distribution of the Milky Way Bulge using APOGEE
• The chemical composition of globular clusters in the Local Group
• Diagnostics of Stellar Modelling from Spectroscopy and Photometry of Globular Clusters
• Photospheric diagnostics of core helium burning in giant stars
• On Lithium-Rich Red Giants. II. Engulfment on the Giant Branch of Trumpler 20
• A phenomenological modification of thermohaline mixing in globular cluster red giants
• Carbon and nitrogen abundances of individual stars in the Sculptor dwarf spheroidal galaxy
• Explaining the multiple populations in globular clusters by multiple episodes of star formation and enrichment without gas expulsion from massive star feedback
• Detailed abundances from integrated-light spectroscopy: Milky Way globular clusters
• Light-Element Abundance Variations at Low Metallicity: the Globular Cluster NGC 5466
• Carbon-enhanced Metal-poor Stars in SDSS/SEGUE. II. Comparison of CEMP Star Frequencies with Binary Population Synthesis Models
• Evidence of extra-mixing in field giants as traced by lithium and carbon isotope ratio
• Precise Masses, Ages of ~1.0 million RGB and RC stars observed by the LAMOST
• Identification, mass and age of primary red clump stars from spectral features derived with the LAMOST DR7
• Light Element Abundances and Multiple Populations in M10
• From the Inner to Outer Milky Way: A Photometric Sample of 2.6 Million Red Clump Stars
• Evidence for C and Mg variations in the GD-1 stellar stream
• Thermohaline mixing in extremely metal-poor stars
• Modelling of integrated-light spectra from the optical to the near-infrared: the globular cluster G280 in M31
• Carbon Abundance Inhomogeneities and Deep Mixing Rates in Galactic Globular Clusters
• UVIT study of UV bright stars in the globular cluster NGC 4147
• Weighing stars from birth to death: mass determination methods across the HRD
• Carbon Abundance of Globular Cluster M22 (NGC 6656) and the Surface Carbon Depletion Rates of the Milky Way Globular Clusters
• CN and CO Features: Key Indicators of Red Giant Evolutionary Phase in Moderate-Resolution X-Shooter Spectra
• Light Element Abundances and Multiple Populations in M53