A detailed study of the main sequence of the Globular Cluster NGC 6397: can we derive constraints on the existence of multiple population?

Abstract

If NGC 6397 contains a large fraction of "second generation" stars (>70% according to recent analysis), the helium abundance of its stars might also be affected, show some star-to-star variation, and be larger than the standard Big Bang abundance Y~0.24. Can we derive constraints on this issue from the analysis of the main sequence width and from its luminosity function? We build up new models for the turnoff masses and the main sequence down to the hydrogen burning minimum mass, adopting two versions of an updated equation of state (EOS) including the OPAL EOS. Models consider different initial helium and CNO abundances to cover the range of possible variations between the first and second generation stars. We compare the models with the observational main sequence. We also make simulations of the theoretical luminosity functions, for different choices of the mass function and of the mixture of first and second generation stars, and compare them with the observed luminosity function, by means of the Kolmogorov Smirnov --KS-- test. The study of the width of the main sequence at different interval of magnitude is consistent with the hypothesis that both generations are present in the cluster. If the CNO increase suggested by spectroscopic observation is taken into account the small helium spread of the main sequence in NGC 6397 implies a substantial helium uniformity (DY~0.02) between first and second generation stars. The possible spread in helium doubles if an even larger increase of CNO is considered. The luminosity function is in any case well consistent with the observed data.

13 pages, 13 figures, accepted for publication to A&A

References in corpus (18)

• Na-O Anticorrelation and HB. VII. The chemical composition of first and second-generation stars in 15 globular clusters from GIRAFFE spectra
• Fast rotating massive stars and the origin of the abundance patterns in galactic globular clusters
• Intrinsic iron spread and a new metallicity scale for Globular Clusters
• Formation and Dynamical Evolution of Multiple Stellar Generations in Globular Clusters
• Na-O Anticorrelation and HB. VIII. Proton-capture elements and metallicities in 17 globular clusters from UVES spectra
• The ACS Survey of Galactic Globular Clusters. I. Overview and Clusters Without Previous HST Photometry
• Updated Electron-Conduction Opacities: The Impact on Low-Mass Stellar Models
• Massive binaries as the source of abundance anomalies in globular clusters
• The ACS Survey of Galactic Globular Clusters. III. The Double Subgiant Branch of NGC 1851
• Signatures of intrinsic Li depletion and Li-Na anti-correlation in the metal-poor globular cluster NGC6397
• Atomic Diffusion and Mixing in Old Stars I. VLT/FLAMES-UVES Observations of Stars in NGC 6397
• The White Dwarf Cooling Sequence of NGC6397
• The fraction of second generation stars in Globular Clusters from the analysis of the Horizontal Branch
• Deep ACS Imaging in the Globular Cluster NGC 6397: The Cluster Color Magnitude Diagram and Luminosity Function
• The C+N+O abundances and the splitting of the subgiant branch in the Globular Cluster NGC 1851
• Probing the Faintest Stars in a Globular Star Cluster
• Deep ACS Imaging in the Globular Cluster NGC6397: Dynamical Models
• Updated Pre-Main Sequence tracks at low metallicities for 0.1< M/Mo<1.5

Cited by in corpus (23)

• Multiple populations in globular clusters. Lessons learned from the Milky Way globular clusters
• Accurate distances to Galactic globular clusters through a combination of Gaia EDR3, HST and literature data
• What is a globular cluster? An observational perspective
• A WFC3/HST view of the three stellar populations in the Globular Cluster NGC6752
• A Double Main Sequence in the Globular Cluster NGC 6397
• Tracing the evolution of NGC6397 through the chemical composition of its stellar populations
• The role of super-asymptotic giant branch ejecta in the abundance patterns of multiple populations in globular clusters
• Helium and Multiple Populations in the Massive Globular Cluster NGC6266 (M62)
• The helium spread in the Globular cluster 47 Tuc
• NGC 2419: a large and extreme second generation in a currently undisturbed cluster
• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. IV. Helium content and relative age of multiple stellar populations within NGC 6352
• The hot horizontal-branch stars in omega Centauri
• Stellar Models of Multiple Populations in Globular Clusters. I. The Main Sequence of NGC 6752
• The mosaic multiple stellar populations in $\omega$ Centauri : the Horizontal Branch and the Main Sequence
• Observing multiple stellar populations with FORS2@VLT - Main sequence photometry in outer regions of NGC 6752, NGC 6397, and NGC 6121 (M 4)
• Deep HST Imaging in NGC 6397: Stellar Dynamics
• The white dwarf population of NGC 6397
• The helium abundance in the metal-poor globular clusters M30 and NGC6397
• The Be-test in the Li-rich star \#1657 of NGC 6397: evidence for Li-flash in RGB stars?
• The white dwarf cooling sequence of NGC 6791: a unique tool for stellar evolution
• Euclid: Early Release Observations -- Unveiling the morphology of two Milky Way globular clusters out to their periphery
• Isochrone fitting of Galactic globular clusters -- V. NGC6397 and NGC6809 (M55)
• Evolution of long-lived globular cluster stars IV. Initial helium content and white-dwarf properties