Gclusters :: Bibliographic item "gc394"

Release 11.12 ("Hergest Ridge")

Gclusters :: Bibliographic item "gc394"

Article ID: gc394

Author Hargis, Jonathan R.; Sandquist, Eric L.; Bolte, Michael

Title The Luminosity Function and Color-Magnitude Diagram of the Globular Cluster M12
Journal The Astrophysical Journal, Volume 608, Issue 1, pp. 243-260
Year of publication 2004 (on gclusters from 2013-10-21 10:33:21 )

Abstract n this paper we present the V and I luminosity functions and color-magnitude diagrams derived from wide-field (23'×23') BVI photometry of the intermediate-metallicity ([Fe/H]~-1.3) Galactic globular cluster M12. Using observed values (and ranges of values) for the cluster metallicity, reddening, distance modulus, and age, we compare these data with recent ?-enhanced stellar evolution models for low-mass metal-poor stars. We describe several methods of making comparisons between theoretical and observed luminosity functions to isolate the evolutionary timescale information that the luminosity functions contain. We find no significant evidence of excesses of stars on the red giant branch, although the morphology of the subgiant branch in the observed luminosity function does not match theoretical predictions in a satisfactory way. Current uncertainties in Teff-color transformations (and possibly also in other physics inputs to the models) make more detailed conclusions about the subgiant branch morphology impossible. Given the recent constraints on cluster ages from the WMAP experiment, we find that good-fitting models that do not include He diffusion (both color-magnitude diagrams and luminosity functions) are too old (by ~1-2 Gyr) to adequately represent the cluster luminosity function. The inclusion of helium diffusion in the models provides an age reduction (compared with nondiffusive models) that is consistent with the age of the universe being 13.7+/-0.2 Gyr.

Tags NGC 6218
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Article ID: gc394
Author	Hargis, Jonathan R.; Sandquist, Eric L.; Bolte, Michael
Title	The Luminosity Function and Color-Magnitude Diagram of the Globular Cluster M12
Journal	The Astrophysical Journal, Volume 608, Issue 1, pp. 243-260
Year of publication	2004 (on gclusters from 2013-10-21 10:33:21 )
Abstract	n this paper we present the V and I luminosity functions and color-magnitude diagrams derived from wide-field (23'×23') BVI photometry of the intermediate-metallicity ([Fe/H]~-1.3) Galactic globular cluster M12. Using observed values (and ranges of values) for the cluster metallicity, reddening, distance modulus, and age, we compare these data with recent ?-enhanced stellar evolution models for low-mass metal-poor stars. We describe several methods of making comparisons between theoretical and observed luminosity functions to isolate the evolutionary timescale information that the luminosity functions contain. We find no significant evidence of excesses of stars on the red giant branch, although the morphology of the subgiant branch in the observed luminosity function does not match theoretical predictions in a satisfactory way. Current uncertainties in Teff-color transformations (and possibly also in other physics inputs to the models) make more detailed conclusions about the subgiant branch morphology impossible. Given the recent constraints on cluster ages from the WMAP experiment, we find that good-fitting models that do not include He diffusion (both color-magnitude diagrams and luminosity functions) are too old (by ~1-2 Gyr) to adequately represent the cluster luminosity function. The inclusion of helium diffusion in the models provides an age reduction (compared with nondiffusive models) that is consistent with the age of the universe being 13.7+/-0.2 Gyr.
Tags	NGC 6218