An empirical calibration of the mixing-length parameter alpha

Abstract

We present an empirical calibration of the Mixing-Length free parameter $\alpha$ based on a homogeneous Infrared database of 28 Galactic globular clusters spanning a wide metallicity range (-2.15$<$[Fe/H]$<$-0.2). Empirical estimates of the red giant effective temperatures have been obtained from infrared colors. Suitable relations linking these temperatures to the cluster metallicity have been obtained and compared to theoretical predictions. An appropriate set of models for the Sun and Population II giants have been computed by using both the standard solar metallicity $[Z/X{]}_{\odot }=0.0275$ and the most recently proposed value $[Z/X{]}_{\odot }=$0.0177. We find that when the standard solar metallicity is adopted, a unique value of $\alpha$=2.17 can be used to reproduce both the solar radius and the population II red giant temperature. Conversely, when the new solar metallicity is adopted, two different values of $\alpha$ are required: $\alpha =1.86$ to fit the solar radius and $\alpha \approx 2.0$ to fit the red giant temperatures. However, it must be noted that, regardless the adopted solar reference, the $\alpha$ parameter does not show any significant dependence on metallicity.

15 pages, 3 figures, ApJ in press

References in corpus (25)

• Abundances for Globular Cluster Giants: I. Homogeneous Metallicities for 24 Clusters
• A Reappraisal of the Solar Photospheric C/O Ratio
• The YY Isochrones for alpha-element Enhanced Mixtures
• The giant, horizontal and asymptotic branches of galactic globular clusters. I. The catalog, photometric observables and features
• The "Solar Model Problem" Solved by the Abundance of Neon in Stars of the Local Cosmos
• A new IR-Array photometric survey of Galactic Globular Clusters: A detailed study of the RGB sequence as a step towards the global testing of stellar models
• The initial Helium content of Galactic Globular Cluster stars from the R-parameter: comparison with the CMB constraint
• The First Detailed Abundances for M giants in Baade's Window from Infrared Spectroscopy
• What Is The Neon Abundance Of The Sun?
• The Red Giant Branch in the Near-Infrared Colour-Magnitude Diagrams. I: The calibration of photometric indices
• Towards the absolute planes: a new calibration of the Bolometric Corrections and Temperature scales for Population II Giants
• An abundance analysis for four Red Horizontal Branch Stars in the extremely metal rich globular cluster NGC 6528
• Broad-band photometric colors and effective temperature calibrations for late-type giants. I. Z=0.02
• High resolution infrared spectra of bulge globular clusters: Liller~1 and NGC 6553
• The Red Giant Branch in Near-Infrared Colour-Magnitude Diagrams. II: The luminosity of the Bump and the Tip
• High resolution infrared spectra of bulge globular clusters: The extreme chemical abundances of Terzan 4 and Terzan 5
• Gemini-Phoenix infrared high-resolution abundance analysis of five giants in the bulge globular cluster NGC 6553
• The Metal Content of the Bulge Globular Cluster NGC 6528
• High resolution infrared spectra of NGC 6342 and NGC 6528: two moderately reddened Bulge Globular Clusters
• Does the Sun Shine by pp or CNO Fusion Reactions?
• Near-Infrared photometry of four metal-rich Bulge globular clusters: NGC6304, NGC6569, NGC6637, NGC6638
• Near-Infrared photometry and spectroscopy of NGC 6539 and UKS 1: two intermediate metallicity Bulge Globular Clusters
• Abundances of Stars in the Galactic Bulge Obtained Using the Keck Telescope
• TNG Near-IR Photometry of five Galactic Globular Clusters
• IR photometric properties of Red Giants in omega Cen

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