The Analysis of Isochrone Fitting Methods for Red Giant Branch Photometry, and Tip Red Giant Branch Distance Determination

摘要

We consider the procedure of isochrone fitting and its application to thestudy of red giant branch (RGB) photometry in old stellar populations. This isextended to consider the problems introduced by the inclusion oflower-magnitude regions of the Colour Magnitude Diagram (CMD). We referespecially to our previous paper Frayn & Gilmore (2002), where the details ofour isochrone interpolation and fitting code are explained. We address the systematic errors inherent in the process of isochronefitting, and investigate the extent to which simple stellar populations can berecovered from noisy photometric data. We investigate the effects caused byinaccurate distance estimates, isochrone model variation and photometricerrors. We present results from two studies of approximately coeval stellarpopulations, those of the Milky Way Globular Cluster System (MWGCS), and theUrsa Minor dwarf spheroidal galaxy. In addition, we introduce a new method for estimating distances usingphotometry of the tip of the RGB which is significantly more robust than thestandard edge-detection filter.