K-band Absolute Magnitude Relations of Red Clump Stars Separated by Age

Abstract

Red clump (RC) stars form a distinguishable clump on the color-magnitude diagram, making it a good distance indicator. Currently, the two main absolute magnitude estimation methods in the I-band (700–900 nm) conflict: one assumes a constant RC magnitude as supported by empirical data and one relates magnitude with other physical characteristics as supported by theoretical models. Studies attribute these discrepancies to population effects, such as dust, and recommend the K-band (2000–2400 nm) to minimize them. Past studies analyzed relations between the K-band magnitude, color, metallicity, and age, including those stratified by age at 2 Gyr. This study aims to investigate these different relations to clarify trends from past studies, discover new trends, and compare them to similar relations in the I-band. After analyzing cluster RC data from Gaia DR3, 2MASS, and Gaia-ESO DR5, K-band magnitude exhibits insignificant correlation in all relations (p>0.05) but has the greatest dependence and the least root mean square error (RMS) with metallicity in the old RC. Significant correlation was found between I-band magnitude and metallicity for all RC and young RC (p<0.05), especially the latter (R2 = 0.804). This consistency with theoretical trends suggests weaker I-band population effects than previously believed. Overall, these three relations yield more accurate predictions than the mean magnitude. Thus, studies cannot solely rely on the mean K-band or I-band magnitude to estimate distance, and magnitude relations stratified by age can potentially lead to more accurate RC distance estimations and a more accurately calibrated distance ladder.