Long period variables detected by ISO in the Small Magellanic Cloud

This article presents the study of the light–curves extracted from the MACHO database of a sample of stars observed by the Infrared Space Observatory in the Small Magellanic Cloud. These stars belong to the ISO–Mini-Survey catalogue of the Magellanic Clouds (ISO–MCMS, Loup et al. in preparation). Most of them are in the asymptotic giant branch (AGB) and supergiant phases. The dominant period and amplitude of pulsation have been derived and the stars have been classified as Mira or Semi–Regular pulsators. Furthermore, the cross–identification with near–infrared DENIS and 2MASS magnitudes available within the ISO–MCMS allowed us: (i) to investigate the properties of these stars in the combined near– and mid–infrared colour–magnitude diagrams, (ii) to derive the bolometric magnitude by integrating the spectral energy distribution and (iii) to estimate the mass–loss rate. The stars have been divided into carbon– (C–) and oxygen–rich (O–rich) using the (J − KS , KS ) colour–magnitude diagram and their period and amplitude distributions have been compared. C–rich AGB stars have a sharp peak in their period distribution at about 250 days and have on average a larger amplitude than O–rich AGB stars. This effect, not previously detected from the study of similar stars in the Large Magellanic Cloud and in the Baade’s window, might be closely related to the metallicity of the environment in which the stars have formed.