Pulsation properties of C stars in the Small Magellanic Cloud

A sample of carbon-rich stars (C-stars) in the Small Magellanic Cloud (SMC) was selected from the combined 2MASS and DENIS catalogues on the basis of their J- K-s colour. This sample was extended to include confirmed C-stars from the Rebeirot et al. ( 1993) spectroscopic atlas. In this combined sample (N = 1149), a smaller number ( N = 1079) were found to have MACHO observations. For this sub- sample, light curves were determined and 919 stars were found to have high quality light-curves with amplitudes of at least 0.05 mag. Of these stars, only 4% have a well-defined single period-most of these have multiple well-defined periods, while 15% have highly irregular light-curves. The distribution of the logarithm of the period versus magnitude, colour, period ratio ( if applicable), and amplitude was analyzed and compared with previous works. Variable C-stars are distributed in three sequences: B, C, and D from Wood et al. ( 1999), and do not populate sequences with periods shorter than log P similar to 1.5. Stellar ages and masses were estimated using stellar evolutionary models.