On main sequence distances and the local distance scale

Abstract

We analyze a deep CMD for the LMC cluster NGC1831, based on CTIO PFCCD frames. More than 4 magnitudes of main sequence (MS) are evident, as well as a prominent clump, and a few possible giant branch stars. We fit the MS to a series of models and Galactic clusters, and derive a distance of 18.3±0.1 and an age of 0.5±0.1 Gyr, for an abundance of about 2/3 solar ([Fe/H]~–0.23), based on the VandenBerg models (Vandenberg and Poll 1989). A fit to the empirical Pleiades MS, assuming an intrisic modulus of 5.6, gives a LMC modulus of 18.25-18.35, after an adjustment for the relative abundance difference of −0.2.