From the Light Curves of Long Period Variables to Their Evolution along the Asymptotic Giant Branch

Abstract A sample of 116 long period variables is studied with the aim to reveal relations between the properties of their light curves and of their evolution along the asymptotic giant branch (AGB). Each light curve is carefully scrutinized, and its properties are summarized in a set of five parameters. One of these, which measures the relative width of the light maxima and minima, is found to be particularly efficient at revealing significant correlations with the current state of the star on the AGB. The picture that had been sketched in an earlier work is clarified, and new features are revealed. In particular, the evolution on the AGB of stars having not yet experienced a third-dredge-up event is shown to go together with a closely related path followed by the light curve in the parameter space. Moreover, evidence is found for the existence of two different types of light curves for stars having experienced dredge-up events strong enough for their impact to be detectable. For some, probably associated with higher initial mass stars, the light maximum becomes broader as the star evolves along the AGB, while for others it becomes narrower. Interpretations are proposed, however, often too speculative to be firmly ascertained: the results presented raise several unanswered questions and point to the need for new observations and analyses, suggesting that light curves still carry more messages and information than have been currently possible to decrypt.