Red variables in the OGLE-II database. II. Comparison of the Large and Small Magellanic Clouds

Abstract

We present period-luminosity relations for more than 3,200 red variable stars in the Small Magellanic Cloud observed in the second phase of the Optical Gravitational Lensing Experiment (OGLE-II). Periods of multiply-periodic light curve solutions combined with the single-epoch 2MASS JHK_S magnitudes, reveal very similar distributions to those for the Large Magellanic Cloud in Paper I. The main features include four pulsating Asymptotic Giant Branch (AGB) ridges, three distinct short-period sequences below the tip of the Red Giant Branch and two long-period sequences of ambiguous origin. We derive a relative distance modulus of the Clouds from the period-luminosity distributions for all stars of Delta mu_0=0.44 mag, which is in good agreement with recent independent results. The tip of the Red Giant Branch shows a colour and metallicity dependence that is in excellent agreement with the empirical results for globular clusters. We conclude that most variable stars below the TRGB are indeed RGB stars.