The Role of Internal Photons on the Chemistry of the Circumstellar Envelopes of AGB Stars

Abstract

Recent high spatial resolution observations of gas and dust in the circumstellar envelopes (CSEs) of AGB stars indicate morphologies much more complex than the smooth density distributions generated by spherically symmetric, constant mass-loss rates. In particular, the observation of spiral arcs and disks indicates the likely presence of a binary companion that in some cases gives rise to the UV photons detected by Galaxy Evolution Explorer . In this paper, we extend our recent model of the chemistry in a clumpy, porous CSE around an AGB star to include the influence of stellar blackbody photons on the CSE chemistry. Our results indicate that internal photons, in a clumpy, porous CSE, can alter chemistry within a few stellar radii and, for some molecules, alter abundances out to several hundred stellar radii. They further suggest that harder radiation from companion stars or accretion disks will have a substantial impact on chemistry in the dust formation zones and inner CSEs of AGB stars.