Atomic and molecular hydrogen in the circumstellar envelopes of late-type stars

Details Atomic and molecular hydrogen in the circumstellar envelopes of late-type stars Atomic and molecular hydrogen in the circumstellar envelopes of late-type stars

May 1983

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1983mnras.203..517g&link_type=abstract

Monthly Notices of the Royal Astronomical Society (ISSN 0035-8711), vol. 203, May 1983, p. 517-532. Research supported by the Re

Astronomy and Astrophysics

Astronomy

54

Hydrogen Atoms, Late Stars, Stellar Envelopes, Atmospheric Models, Galactic Radiation, Molecules, Photodissociation, Photosphere, Ultraviolet Radiation

Scientific paper

The distribution of atomic and molecular hydrogen in the expanding circumstellar envelopes of cool evolved stars is discussed. The main concern is to evaluate the effects of photodestruction of H2 by galactic UV radiation, including shielding of the radiation by H2 itself and by dust in the envelope. One of the most important parameters is the H/H2 ratio which is frozen out in the upper atmosphere of the star. For stars with photospheric temperatures greater than about 2500 K, atmospheric models suggest that the outflowing hydrogen is mainly atomic, whereas cooler stars should be substantially molecular. In the latter case, photodissociation of H2 and heavy molecules contribute to the atomic hydrogen content of the outer envelope. The presented estimates indicate that atomic hydrogen is almost at the limit of detection in the C-rich star IRC + 10216, and may be detectable in warmer stars. Failure to detect it would have important implications for the general understanding of circumstellar envelopes.

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