The Araucaria Project. Population effects on the V and I band magnitudes of red clump stars

TL;DR

This study investigates how population differences influence the V and I band magnitudes of red clump stars across 23 nearby galaxies, revealing significant effects that challenge their use for precise distance measurements in optical bands.

Contribution

It provides empirical evidence confirming theoretical predictions about population effects on red clump magnitudes and highlights the superiority of near-infrared photometry for distance estimation.

Findings

Population effects significantly impact red clump magnitudes in V and I bands.

Optical photometry of red clump stars is unreliable for distance measurements without better calibration.

Near-infrared photometry offers a more accurate method for galaxy distance determination.

Abstract

We present measurements of the V and I band magnitudes of red clump stars in 15 nearby galaxies obtained from recently published homogenous HST photometry. Supplementing these results with similar data for another 8 galaxies available in the literature the populational effects on the V and I band magnitudes of red clump stars were investigated. Comparing red clump magnitudes with the I-band magnitude of the TRGB in a total sample of 23 galaxies possessing very different environments we demonstrate that population effects strongly affect both the V and I band magnitude of red clump stars in a complex way. Our empirical results basically confirm the theoretical results of Girardi and Salaris, and show that optical (VI) photometry of red clump stars is not an accurate method for the determination of distances to nearby galaxies at the present moment, as long as the population effects are not better calibrated, both empirically and theoretically. Near infrared photometry is a much better way to measure galaxy distances with red clump stars given its smaller sensitivity to population effects.