The Impact of Contaminated RR Lyrae/Globular Cluster Photometry on the Distance Scale

TL;DR

This paper investigates how contaminated photometry of RR Lyrae stars in globular clusters affects the accuracy of the cosmic distance scale, emphasizing the importance of accounting for radial-dependent photometric errors.

Contribution

It highlights the impact of clustercentric distance-dependent photometric contamination on distance measurements and aims to improve the reliability of the cosmic distance scale.

Findings

Photometric contamination varies with clustercentric distance.

Contamination affects key parameters like distance and magnitude.

Awareness of contamination is crucial for accurate measurements.

Abstract

RR Lyrae variables and the stellar constituents of globular clusters are employed to establish the cosmic distance scale and age of the universe. However, photometry for RR Lyrae variables in the globular clusters M3, M15, M54, M92, NGC2419, and NGC6441 exhibit a dependence on the clustercentric distance. For example, variables and stars positioned near the crowded high-surface brightness cores of the clusters may suffer from photometric contamination, which invariably affects a suite of inferred parameters (e.g., distance, color excess, absolute magnitude, etc.). The impetus for this study is to mitigate the propagation of systematic uncertainties by increasing awareness of the pernicious impact of contaminated and radial-dependent photometry.