Pulsation properties of C stars in the Small Magellanic Cloud

Abstract

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 = 1152), 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 $\log P \sim 1.5$. Stellar ages and masses were estimated using stellar evolutionary models.

18 pages, 22 figures, 3 tables, A&A Accepted (2005 March 18), added a reference, corrected typos