Introduction

Red giant stars are probably the least understood of all variable stars. Although o Ceti (Mira) was the first recorded pulsating star, and the Miras have by far the largest visual amplitudes of any class of pulsating star, even the mode of pulsation of these stars has remained a topic of controversy (e.g. Wood 1995, Bedding et al. 1998). All this has changed with the arrival of the MACHO survey of variable stars in the LMC: some problems have been solved, but unexpected new ones have turned up. In this paper, the results of the study of a complete sample of red giant stars in a 0.5 x 0.5 degree area of the LMC bar are discussed. A more detailed description of the MACHO data is given in Wood et al. (1999) and Alcock et al. (2000).

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