Chemical structure of circumstellar shells

Journal Article · Tue Jul 15 04:00:00 EDT 1980 · Astrophys. J., Lett. Ed.; (United States)

DOI:https://doi.org/10.1086/183295· OSTI ID:6782842

Scalo, J M; Slavsky, D B

We discuss nonequilibrium chemistry in isotropic models of expanding circumstellar shells surrounding oxygen-rich red giant stars, using time-scale arguments and chemical kinetic calculations. We predict that most observable molecules should attain significant abundances only beyond a critical radius, approx.3 x 10/sup 14/ cm for low-density shells; beyond that limit H/sub 2/O is efficiently photo-dissociated by interstellar ultraviolet radiation. We show that observation of SiS should give an unambiguous limit to the fraction of circumstellar silicon tied up in grains if chromospheric radiation is unimportant, while SiO is unsuitable for this purpose. Photodissociation of H/sub 2/O by chromospheric radiation may be important in the inner part of the shell, and it is suggested that observations of molecular column densities of H/sub 2/O and other molecules in shells may be used to constrain chromospheric models for red giants.

• Research Organization: Department of Astronomy, University of Astronomy at Austin
• OSTI ID: 6782842
• Journal Information: Astrophys. J., Lett. Ed.; (United States), Journal Name: Astrophys. J., Lett. Ed.; (United States) Vol. 239:2; ISSN AJLEA
• Country of Publication: United States
• Language: English

Related Subjects

640102* -- Astrophysics & Cosmology-- Stars & Quasi-Stellar
Radio & X-Ray Sources
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ABUNDANCE
ATMOSPHERES
CHEMICAL COMPOSITION
CHEMICAL REACTIONS
CHEMISTRY
DISSOCIATION
ELECTROMAGNETIC RADIATION
ELEMENTS
GIANT STARS
HYDROGEN COMPOUNDS
HYDROXIDES
INTERSTELLAR GRAINS
MOLECULES
NONMETALS
OXYGEN
OXYGEN COMPOUNDS
PARTICLES
PHOTOCHEMISTRY
RADIATIONS
RED GIANT STARS
SEMIMETALS
SILICON
STARS
STELLAR ATMOSPHERES
ULTRAVIOLET RADIATION
WATER