The Intrinsic I-Band Magnitude Dispersion of the Galactic Bulge Red Clump

TL;DR

This study measures the intrinsic I-band magnitude dispersion of the Galactic bulge red clump, finding it to be around 0.17 mag, which impacts models of the bulge's structure and evolution.

Contribution

It provides the first precise estimates of the intrinsic magnitude dispersion of the Galactic bulge red clump using two independent methods.

Findings

Intrinsic dispersion is approximately 0.17 mag.

Results constrain the bar's orientation and length estimates.

Dispersion exceeds predictions from metallicity effects alone.

Abstract

We measure the intrinsic magnitude dispersion of the Galactic bulge red clump (RC) using two different methods and arrive at an estimate of \sigma_{I} ~ 0.17 mag. We first estimate the width of the RC by analyzing in detail a sample of RC measurements toward double RC sightlines, which are toward regions of the bulge that are geometrically thin. We obtain \sigma_{I} ~ 0.17 mag. We then estimate the value by comparing the luminosity function for bulge RC and red giant (RG) stars in V to that in I for a sightline near the plane, and we obtain a value of \sigma_{I} ~ 0.14-0.17 mag. This result has structural and evolutionary repercussions. It constrains model estimates of the bar's orientation angle derived from RC studies as well as the inferred characteristic length of the bar for a given characteristic height. Moreover, the value is too large to account for using the predicted evolutionary effects of the known metallicity distribution, implying the presence of other population effects.