The variability of Magellanic cluster infrared stars

Abstract

We report on the light variations of the infrared stars that were discovered recently in the Magellanic clusters NGC 419, 1783 and 1978. Their periods, of 528, 458 and 491 days, are among the longest known for carbon-rich Mira variables in the Clouds. All three IR stars were found to lie on the extension of the period-Mbol relation derived from the shorter-period C-rich Miras while they were 0.45–0.70 mag fainter than the extension of the period-MK relation. Their main sequence masses were determined by isochrone fitting to be 1.5–1.6 M⊙, consistent with the prediction of the evolutionary models of Vassiliadis & Wood.