Multiwavelength Absolute Magnitudes and Colors of Red Clump Stars in the Gaia Era

This study presents the multiwavelength investigation of the absolute magnitudes and colors of the red clump (RC) stars selected from APOGEE and GALAH DR2 combined catalog which is complemented with Gaia DR2 astrometric data and multiwavelength photometric data of GALEX GR6/7, SDSS DR7, Gaia DR2, 2MASS, and WISE sky surveys. The analyses are centered on the different distance estimation methods using Gaia trigonometric parallaxes, (1/& x3d6;) and Bayes statistics, and chemically defined Galactic disk populations on [alpha/Fe] x [Fe/H] plane. This investigation questions the long-studied problem of the population effects on RC luminosity. Using two different distance estimation approaches, (i) chemical thin and chemical thick disk RC stars are shown to have different absolute magnitudes, while colors remain the same in all photometric bands. Absolute magnitudes vary between -0.12 and +0.13 mag for the 1/& x3d6; with the change of the Galactic population. This variation in absolute magnitudes is found to be larger for the other method, (ii) the Besancon population synthesis model of Galaxy for 2MASS photometry, in which the absolute magnitude difference between chemical populations were found between -0.35 and -0.40 mag from thin disk to thick disk. When results compared with each other, differences of absolute magnitudes are about three times larger in the model than in the observations. We confirm that the RC absolute magnitudes depend on alpha-element abundances of Galactic populations.