Infrared Giants

Abstract

Towards the end of their lives, many stars become enshrouded in an envelope of self-created dust, thereby becoming faint and wellnigh unobservable optically, but bright and prominent on the infrared sky. The observational indications are that this intrinsically intriguing phenomenon is also associated with a fractionally large cumulative mass loss and thus signals a decisive turning point in a star’s evolutionary history. As such, the incorporation of this phenomenon and the concomitant mass loss into stellar evolution codes is evidently highly desirable. Among the important issues whose proper quantitative investigation would then be facilitated are the following: the upper mass limit on the main sequence for ultimate evolution into white dwarfs; the mass function for white dwarfs; the structure of the immediate progenitors of planetary nebulae; and the chemical and particulate enrichment of the interstellar medium. A useful review of these topics in the context of the theory of asymptotic giant branch (AGB) stars has been given by Iben and Renzini (1983).