The Araucaria Project: Dependence of MeanK,J, andIAbsolute Magnitudes of Red Clump Stars on Metallicity and Age

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Abstract
(Abridged) We present results of deep near-infrared JK imaging of LMC, SMC, and the Carina and Fornax dwarf galaxies. A comparison of the extinction-corrected K-band red clump star magnitudes with the tip of the red giant branch magnitude, the mean RR Lyrae star V-band magnitude, and the mean K-band magnitude of Cepheid variables at a period of 10 days (for the LMC and SMC) strongly suggest that the red clump star absolute K-band magnitude has a very low (if any) dependence on metallicity over the broad range of metallicities covered by our target galaxies. This finding is in contrast to the mean I-band and J-band red clump star magnitudes, which do have a clear metallicity dependence which we calibrate from our data. Excellent agreement with the former calibration of the red clump I-band magnitude dependence on metallicity of Udalski is found from our new data. We use the Galactic cluster K-band red clump star data of Grocholski and Sarajedini to demonstrate that the K-band red clump star absolute magnitude also has very little (if any) dependence on age. The present study therefore provides clear evidence that the mean K-band magnitude of red clump stars is an excellent distance indicator, with very small (if any) population corrections to be applied over a large range in metallicity and age. Comparing derived distances to those coming from the observed mean I-band magnitudes of the red clump stars, we find evidence that there is likely to be a problem in the photometric calibration of the local, solar neighborhood red clump star K-band or I-band magnitudes which amounts to some 0.2 mag. A re-determination of the absolute photometric calibration of the Hipparcos-observed nearby red clump stars seems necessary to resolve this problem.

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