How Do Pulsating Giant Stars Make Dust? (Abstract)

Volume 37 number 2 (2009)

Lee Anne Willson

Abstract

(Abstract only) Mira variables of spectral types M (more oxygen than carbon), S (carbon ≈ oxygen), and C (more carbon than oxygen) all show signs of dusty winds. Radiative acceleration of the dust is thought to play a crucial role in driving the winds, once the atmosphere has been levitated by the pulsation. However, efforts to model the nucleation and growth of dust grains have encountered a host of difficulties. The process is complex, involving a very large number of reactions of particles (atoms, molecules, clusters, and grains) with each other. The coupling of the grains to the radiation field is also difficult to model with confidence, as it depends on the composition, the size, and the shape of the grains. Common approximations to make the problem tractable have lead to results that contradict observations; for example, they predict that S stars should produce no dust, but some S stars do. Some ideas for solving this problem come from laboratory studies. There may also be ways to get the right result without so much work by taking advantage of natural feedback evident in the models.