The evolution of low-metallicity asymptotic giant branch stars and the formation of carbon-enhanced metal-poor stars

Abstract

We investigate the behaviour of asymptotic giant branch (AGB) stars between metallicities Z = 10-4 and Z = 10-8 . We determine which stars undergo an episode of flash-driven mixing, where protons are ingested into the intershell convection zone, as they enter the thermally pulsing AGB phase and which undergo third dredge-up. We find that flash-driven mixing does not occur above a metallicity of Z = 10-5 for any mass of star and that stars above 2 M do not experience this phenomenon at any metallicity. We find carbon ingestion (CI), the mixing of carbon into the tail of hydrogen burning region, occurs in the mass range 2 M to around 4 M . We suggest that CI may be a weak version of the flash-driven mechanism. We also investigate the effects of convective overshooting on the behaviour of these objects. Our models struggle to explain the frequency of CEMP stars that have both significant carbon and nitrogen enhancement. Carbon can be enhanced through flash-driven mixing, CI or just third dredge up. Nitrogen can be enhanced through hot bottom burning and the occurrence of hot dredge-up also converts carbon into nitrogen. The C/N ratio may be a good indicator of the mass of the primary AGB stars.

15 pages, 13 figures, 1 table, accepted by MNRAS

References in corpus (8)

• Nucleosynthetic signatures of the first stars
• The Frequency of Carbon-Enhanced Metal-Poor Stars in the Galaxy from the HERES sample
• Carbon-Enhanced Metal-Poor Stars. III. Main-Sequence Turn-Off Stars from the SDSS/SEGUE Sample
• Thermohaline mixing and gravitational settling in carbon-enhanced metal-poor stars
• Mass loss and yield uncertainty in low-mass asymptotic giant branch stars
• Light element abundances in carbon-enhanced metal-poor stars
• An Explosive End to Intermediate-Mass Zero-Metallicity Stars and Early Universe Nucleosynthesis
• Carbon Rich Extremely Metal Poor Stars: Signatures of Population-III AGB stars in Binary Systems

Cited by in corpus (45)

• MESA Isochrones and Stellar Tracks (MIST). I: Solar-Scaled Models
• The s Process: Nuclear Physics, Stellar Models, Observations
• The Dawes Review 2: Nucleosynthesis and stellar yields of low and intermediate-mass single stars
• Evolution, nucleosynthesis and yields of low mass AGB stars at different metallicities (II): the FRUITY database
• Galactic Chemical Evolution and solar s-process abundances: dependence on the 13C-pocket structure
• Super and massive AGB stars - IV. Final fates - Initial to final mass relation
• The s process in asymptotic giant branch stars of low metallicity and the composition of carbon-enhanced metal-poor stars
• The s-Process in Low Metallicity Stars. II. Interpretation of High-Resolution Spectroscopic Observations with AGB models
• The intermediate neutron-capture process and carbon-enhanced metal-poor stars
• Super and Massive AGB Stars: II - Nucleosynthesis and Yields - Z=0.02, 0.008 and 0.004
• Population Synthesis of Binary Carbon-enhanced Metal-poor Stars
• s-Process in Low Metallicity Stars. I. Theoretical Predictions
• s-Process in Low Metallicity Stars. III. Individual analysis of CEMP-s and CEMP-s/r with AGB models
• The Stellar Abundances for Galactic Archaeology (SAGA) Database II - Implications for Mixing and Nucleosynthesis in Extremely Metal-Poor Stars and Chemical Enrichment of the Galaxy
• Global non-spherical oscillations in 3-D $4\pi$ simulations of the H-ingestion flash
• 3D hydrodynamical simulations of a proton ingestion episode in a low-metallicity asymptotic giant branch star
• Non standard s-process in massive rotating stars. Yields of $10-150$ $M_{\odot }$ models at $Z=10^{-3}$
• Metal-Poor Stars Observed with the Magellan Telescope I. Constraints on Progenitor Mass and Metallicity of AGB Stars Undergoing s-Process Nucleosynthesis
• Lithium abundances in CEMP stars
• The effects of thermohaline mixing on low-metallicity asymptotic giant branch stars
• Learning about the intermediate neutron-capture process from lead abundances
• Constraints of the physics of low-mass AGB stars from CH and CEMP stars
• Evolution of Low- and Intermediate-Mass Stars with [Fe/H] <= -2.5
• Are some CEMP-s stars the daughters of spinstars?
• The end of super AGB and massive AGB stars I. The instabilities that determine the final mass of AGB stars
• Convective H-He Interactions in Massive Population III Stellar Evolution Models
• Dust formation in the winds of AGBs: the contribution at low metallicities
• The occurrence of nitrogen-enhanced metal-poor stars: implications for the initial mass function in the early Galactic halo
• The intermediate neutron capture process. III. The i-process in AGB stars of different masses and metallicities without overshoot
• Gemini/GRACES Spectroscopy of Stars in Triangulum II
• Searches for Metal-Poor Stars from the Hamburg/ESO Survey using the CH G-band
• [O/Fe] Estimates for Carbon-Enhanced Metal-Poor Stars from Near-IR Spectroscopy
• Evolution and CNO yields of Z=10^-5 stars and possible effects on CEMP production
• A Search for Unrecognized Carbon-Enhanced Metal-Poor Stars in the Galaxy
• Carbon-enhanced Metal-poor Stars in SDSS/SEGUE. II. Comparison of CEMP Star Frequencies with Binary Population Synthesis Models
• A spectroscopic binary in the Hercules dwarf spheroidal galaxy
• Fates of the oldest intermediate-mass stars - Primordial to Extremely Metal-Poor AGB and Super-AGB Stars: White Dwarf or Supernova progenitors
• Modelling the nucleosynthetic properties of carbon-enhanced metal-poor RR Lyrae stars
• Nucleosynthetic yields of Z=$10^{-5}$ intermediate-mass stars
• HCT/HESP study of two carbon stars from the LAMOST survey
• The peculiar abundances of HE 1005-1439. A carbon-enhanced extremely metal-poor star contaminated with products of both s-and i-process nucleosynthesis
• Dust formation and mass loss around intermediate-mass AGB stars with initial metallicity $Z_{\mathrm{ini}}\le 10^{-4}$ in the early Universe I: Effect of surface opacity on the stellar evolution and dust-driven wind
• Spectroscopic study of four metal-poor carbon stars from the Hamburg/ESO Survey: On confirming the low-mass nature of their companions
• Probing the nucleosynthetic contribution of low-metallicity, low-mass star companions of CEMP stars
• A comparative study on three modes of s-process nucleosynthesis in extremely metal-poor AGB stars