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

Abstract

We present period-luminosity relations for more than 3200 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 JHKS 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 (RGB) 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 Δμ 0 = 0.44 mag, which is in good agreement with recent independent results. The tip of the RGB 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 tip of the red giant branch are indeed RGB stars.