A theoretical analysis of the systematic errors in the Red Clump distance to the LMC

Abstract

We present a detailed analysis of the uncertainty on the theoretical population corrections to the LMC Red Clump (RC) absolute magnitude, by employing a population synthesis algorithm to simulate theoretically the photometric and spectroscopic properties of RC stars, under various assumptions about the LMC Star Formation Rate (SFR) and Age Metallicity Relationship (AMR). A comparison of the outcome of our simulations with observations of evolved low-intermediate mass stars in the LMC allows one to select the combinations of SFR and AMR that bracket the real LMC star formation history, and to estimate the systematic error on the associated RC population corrections. The most accurate estimate of the LMC distance modulus from the RC method (adopting the OGLE-II reddening maps for the LMC) is obtained from the K-band magnitude, and provides (m-M)_{0, LMC}=18.47 +/-0.01(random) +0.05/-0.06(systematic). Distances obtained from the I-band, or from the multicolour RC technique which determines at the same time reddening and distance, both agree (albeit with a slightly larger error bar) with this value.