Population II stars and the Spite plateau; Stellar evolution models with mass loss

Abstract

We aim to determine the constraints that observed chemical abundances put on the potential role of mass loss in metal poor dwarfs. Self-consistent stellar evolutionary models that include all the effects of atomic diffusion and radiative accelerations for 28 chemical species were computed for stellar masses between 0.6 and 0.8 Msun. Models with an initial metallicity of Z_0=0.00017 and mass loss rates from 10e-15 Msun to 10e-12 Msun were calculated. They were then compared to previous models with mass loss, as well as to models with turbulent mixing. For models with an initial metallicity of Fe/H=-2.31, mass loss rates of about 10e-12 Msun lead to surface abundance profiles that are very similar to those obtained in models with turbulence. Both models have about the same level of agreement with observations of galactic-halo lithium abundances, as well as lithium and other elemental abundances from metal poor globular clusters such as NGC 6397. In this cluster, models with mass loss agree slightly better with subgiant observations of Li abundance than those with turbulence. Lower red giant branch stars instead favor the models with turbulence. Larger differences between models with mass loss and those with turbulence appear in the interior concentrations of metals. The relatively high mass loss rates required to reproduce plateau-like lithium abundances appear unlikely when compared to the solar mass-loss rate. However the presence of a chromosphere on these stars justifies further investigation of the mass-loss rates.

16 pages, 13 figures, accepted for publication in Astronomy and Astrophysics

References in corpus (19)

• Wilkinson Microwave Anisotropy Probe (WMAP) Three Year Results: Implications for Cosmology
• Primordial Nucleosynthesis in the Precision Cosmology Era
• A Bitter Pill: The Primordial Lithium Problem Worsens
• Thermohaline mixing: A physical mechanism governing the photospheric composition of low-mass giants
• Testing a Predictive Theoretical Model for the Mass Loss Rates of Cool Stars
• A probable stellar solution to the cosmological lithium discrepancy
• First stars VII. Lithium in extremely metal poor dwarfs
• Atomic Diffusion and Mixing in Old Stars I. VLT/FLAMES-UVES Observations of Stars in NGC 6397
• Numerically determined transport laws for fingering ("thermohaline") convection in astrophysics
• Line shift, line asymmetry, and the 6Li/7Li isotopic ratio determination
• Lithium abundance in the globular cluster M4: from the Turn-Off to the RGB Bump
• The First Empirical Mass Loss Law for Population II Giants
• From First Stars to the Spite Plateau: a Possible Reconciliation of Halo Stars Observations with Predictions from Big Bang Nucleosynthesis
• On the Use of Blanketed Atmospheres as Boundary Conditions for Stellar Evolutionary Models
• Atomic Diffusion and Mixing in Old Stars. III. Analysis of NGC 6397 Stars under New Constraints
• Solving the cosmic lithium problems with primordial late-decaying particles
• Sirius A: turbulence or mass loss?
• Abundance anomalies in pre-main-sequence stars: Stellar evolution models with mass loss
• Chromospheres in Metal-Poor Stars Evidenced from the He I 10830A Line

Cited by in corpus (9)

• The influence of atomic diffusion on stellar ages and chemical tagging
• Atomic diffusion and mixing in old stars IV: Weak abundance trends in the globular cluster NGC 6752
• The Gaia-ESO survey: 3D NLTE abundances in the open cluster NGC 2420 suggest atomic diffusion and turbulent mixing at the origin of chemical abundance variations
• Discovery of a thin lithium plateau among metal-poor red giant branch stars
• Matter accretion in metal-poor stars down to extremely metal-poor stars and the lithium problem
• A coherent view of Li depletion and angular momentum transport to explain the Li plateau -- from Population II to Population I stars
• Atomic diffusion and mixing in old stars VII. Abundances of Mg, Ti, and Fe in M30
• The age of the Methuselah star in light of stellar evolution models with tailored abundances
• Chemical element transport in stellar evolution models