The Red Giant Branch Luminosity Function Bump

Abstract

We present observational estimates of the magnitude difference between the luminosity function RGB bump and the HB (Delta(bump-zahb)), and of star counts in the bump region (R_bump), for a sample of 54 Galactic globular clusters (GCs) observed by the HST. The large sample of stars resolved in each cluster, and the high photometric accuracy of the data allowed us to detect the bump also in a number of metal poor clusters. To reduce the photometric uncertainties, empirical values are compared with theoretical predictions obtained from a set of updated canonical stellar evolution models which have been transformed directly into the HST flight system. We found an overall qualitative agreement between theory and observations. Quantitative estimates of the confidence level are hampered by current uncertainties on the GCs metallicity scale, and by the strong dependence of Delta(bump-zahb) on the cluster metallicity. In case of the R_bump parameter, which is only weakly affected by the metallicity, we find a very good quantitative agreement between theoretical canonical models and observations. For our full cluster sample the average difference between predicted and observed R_bump values is practically negligible, and ranges from -0.002 to -0.028, depending on the employed metallicity scale. The observed dispersion around these values is entirely consistent with the observational errors on R_bump. As a comparison, the value of R_bump predicted by theory in case of spurious bump detections would be \~0.10 smaller than the observed ones. We have also tested the influence on the predicted Delta(bump-zahb) and R_bump values of an He-enriched component in the cluster stellar population. We find that the predicted Delta(bump-zahb) and R_bump values are only marginally affected.

11 pages, accepted for publication in A&A

References in corpus (23)

• First Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Determination of Cosmological Parameters
• Abundances for Globular Cluster Giants: I. Homogeneous Metallicities for 24 Clusters
• Distances, ages, and epoch of formation of globular clusters
• The giant, horizontal and asymptotic branches of galactic globular clusters. I. The catalog, photometric observables and features
• Distances and ages of NGC 6397, NGC 6752 and 47 Tuc
• A Globular Cluster Metallicity Scale Based on the Abundance of Fe II
• Galactic Globular Cluster Metallicity Scale from the Calcium Triplet. II. Rankings, Comparisons and Puzzles
• The Charge Transfer Efficiency and Calibration of WFPC2
• Helium variation due to self-pollution among Globular Cluster stars: consequences on the horizontal branch morphology
• HST color-magnitude diagrams of 74 galactic globular clusters in the HST F439W and F555W bands
• Homogeneous age dating of 55 Galactic globular clusters. Clues to the Galaxy formation mechanisms
• Galactic Globular Cluster Relative Ages
• Standard and Non-Standard Plasma Neutrino Emission Revisited
• Red Giant Branch stars: the theoretical framework
• The initial Helium content of Galactic Globular Cluster stars from the R-parameter: comparison with the CMB constraint
• A critical investigation on the discrepancy between the observational and theoretical Red Giant luminosity function "Bump"
• Models for Old, Metal-Poor Stars with Enhanced alpha-Element Abundances. III. Isochrones and Isochrone Population Functions
• Comparison between predicted and empirical DV(Bump -HB) in Galactic Globular Clusters
• The Age Dependent Luminosities of the Red Giant Branch Bump, Asymptotic Giant Branch Bump, and Horizontal Branch Red Clump
• Transformations between the theoretical and observational planes in the HST-NICMOS and WFPC2 photometric systems
• The shape of the Red Giant Branch Bump as a diagnostic of partial mixing processes in low-mass stars
• The effect of diffusion on the Red Giant luminosity function 'bump'
• Global metallicity of globular cluster stars from colour-magnitude diagrams

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• A large stellar evolution database for population synthesis studies. I. Scaled solar models and isochrones
• Galactic Globular Cluster Relative Ages. II
• Transforming observational data and theoretical isochrones into the ACS/WFC Vega-mag system
• The ACS LCID project. III. The star formation history of the Cetus dSph galaxy: a post-reionization fossil
• Multivariate Analysis of Globular Cluster's Horizontal Branch Morphology: searching for the second parameter
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• The Red Giant Branch in Near-Infrared Colour-Magnitude Diagrams. II: The luminosity of the Bump and the Tip
• Red Giant Branch Bump Brightness and Number Counts in 72 Galactic Globular Clusters Observed with the Hubble Space Telescope
• Near-Infrared Photometry of Globular Clusters Towards the Galactic Bulge: Observations and Photometric Metallicity Indicators
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• OGLE-III Detection of the Anomalous Galactic Bulge Red Giant Branch Bump: Evidence of Enhanced Helium Enrichment
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• Helium self--enrichment and the second parameter problem in M3 and M13
• Theoretical Uncertainties in Red Giant Branch Evolution: The Red Giant Branch Bump
• The Red-Giant Branch Bump Revisited: Constraints on Envelope Overshooting in a Wide Range of Masses and Metallicities
• The Gradients in the 47 Tuc Red Giant Branch Bump and Horizontal Branch are Consistent With a Centrally-Concentrated, Helium-Enriched Second Stellar Generation
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• On the Delta V_HB_bump parameter in Globular Clusters
• On the magnitude difference between the main sequence turn off and the red giant branch bump in Galactic globular clusters
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• Near-Infrared photometry of four metal-rich Bulge globular clusters: NGC6304, NGC6569, NGC6637, NGC6638
• Diagnostics of Stellar Modelling from Spectroscopy and Photometry of Globular Clusters
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• From Canonical to Enhanced Extra Mixing in Low-Mass Red Giants: Tidally Locked Binaries
• The ACS LCID project IV: detection of the RGB bump in isolated galaxies of the Local Group
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• The Luminosity Function and Color-Magnitude Diagram of the Globular Cluster M12
• A new identity card for the bulge globular cluster NGC 6440 from resolved star counts
• Investigating the Consistency of Stellar Evolution Models with Globular Cluster Observations via the Red Giant Branch Bump
• The evolutionary status of the blue hook stars in Omega Centauri
• On a new parameter to estimate the helium content in old stellar systems
• Mirror principle and the red-giant bump: the battle of entropy in low-mass stars
• Fluorine Abundance Variations as a Signature of Enhanced Extra Mixing in Red Giants of the Globular Cluster M4
• From Theory to Observations and viceversa: theoretical uncertainties and observational constraints
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