On the Relative Distances of ω Centauri and 47 Tucanae

Abstract

We present precise optical and near-infrared ground-based photometry of two globular clusters (GCs): ω Cen and 47 Tuc. These photometric catalogs are unbiased in the red giant branch (RGB) region close to the tip. We provide new estimates of the RGB tip (TRGB) magnitudes-m 1 (TRGB) p 9.84 ± 0.05, ω Cen; m I (TRGB) p 9.46 ± 0.06, 47 Tuc-and use these to determine the relative distances of the two GCs. We find that distance ratios based on different calibrations of the TRGB, the RR Lyrae stars, and kinematic distances agree with each other within 1 σ. Absolute TRGB and RR Lyrae distance moduli agree within 0.10-0.15 mag, while absolute kinematic distance moduli are 0.2-0.3 mag smaller. Absolute distances to 47 Tuc based on the zero-age horizontal branch and on the white dwarf fitting agree within 0.1 mag, but they are 0.1-0.3 mag smaller than TRGB and RR Lyrae distances. © 2008. The American Astronomical Society. All rights reserved. Printed in U.S.A.