Science with the Atacama Large Millimeter

Extensive post-main sequence mass loss occurs for low and intermediate mass stars on the asymptotic giant branch (AGB), and for the higher mass stars during their red supergiant evolution. These winds aaect the evolution of the stars profoundly, as well as the enrichment of the interstellar medium with heavy elements and grain particles. The mass loss on the AGB is the by far the most well studied, but the basic processes are still not understood or cannot be described in a proper quantitative way, e.g., the mass loss mechanism itself. These objects also provide us with fascinating systems, in which intricate interplays between various physical and chemical processes take place, and their relative simplicity in terms of geometry, density distribution, and kinematics makes them excellent astrophysical laboratories. In this review I will concentrate on the aspects of AGB mass loss which are of particular interest in connection with the ALMA. Stars enter the scene, at least on an average, according to a mass spectrum in the form of a power-law dN=dM / M ? , where depends on the mass range 2.3 for M>0.5 M , Scalo (1998)], with a low mass cut-oo at 0.08M and an upper mass limit at 100 M. The stars will all evolve through the main sequence, and a phase of central He-burning (provided that the mass is above 0.5M), but the subsequent evolution depends strongly on the mass. There is an important dividing line at 6{9M the exact value depends on the treatment of convection, Bressan et al. (1993)]. Less massive stars will develop an electron-degenerate core, and will hence not go through an additional central nuclear-burning unless a gravitational collapse ensues. The eeect of an intense surface mass loss will prevent the latter from happening to stars with masses up to 8M. Stars more massive than about 6{9 M will go through additional central nuclear-burning stages. Thus, the nal evolutionary stellar stage of stars slightly less massive than 10 M (and M >0.5 M) will be that of red giants on the asymptotic giant branch (AGB), while the more massive ones will become supergiants. The nal stellar remnant will be a white dwarf and a neutron star/black hole, respectively. This means that more than 95% of all stars which have left the main sequence and ended their lives as stars during a Hubble time have done so after the AGB evolution. In this …