OH-IR stars. I - Physical properties of circumstellar envelopes

Abstract

view Abstract Citations (364) References (19) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS OH-IR stars. I. Physical properties of circumstellar envelopes. Goldreich, P. ; Scoville, N. Abstract A theoretical model of the circumstellar envelope which surrounds a OH-IR star is developed. The circumstellar gas is ejected by radiation pressure which acts on dust grains that condense in the atmosphere of the central star. The dust grains transfer momentum to the gas by collisions with the gas molecules. These collisions are the dominant source of heat input to the circumstellar gas. The major sources of cooling are the emission of radiation by H20 molecules and adiabatic expansion. The gas temperature decreases from T 2 x l0 K near the stellar surface at r 6 x 1013 cm, to T 8 x 102 K at r = 1015 cm and to T 102 K at r = 1016 cm. The OH molecule abundance in the circumstellar envelope is controlled by chemical exchange reactions and by the dissociation of H20 molecules. The reaction OH + H2 H20 + H + 0.69 eV, which has an activation energy of 0.3 eV, rapidly converts OH molecules into H20 molecules in the warm (T > 5 x 102 K) inner (r <% 2 x 1015 cm) region of the circumstellar envelope. Beyond r 2 x 1015 cm, T is so low that the exchange reaction is very slow and the mean lifetime of an OH molecule is greater than the expansion time scale for the circumstellar envelope. In the outer region of the circumstellar envelope, OH molecules are produced from the photodissociation of H20 molecules by the interstellar ultraviolet radiation and from the dissociation of H20 molecules by collisions with dust grains. These processes are capable of producing OH number densities greater than 1 at r 1016 cm. The predicted values of the gas temperature, T, and the OH abundance, o , depend upon the rate of mass loss from the central star, (t) The results quoted above are based on a calculation with = 3 x l0- M0 yr-1. In general, T varies inversely and o varies directly with (I). Subject headings: infrared: sources - stars: circumstellar shells Publication: The Astrophysical Journal Pub Date: April 1976 DOI: 10.1086/154257 Bibcode: 1976ApJ...205..144G Keywords: Atmospheric Models; Hydroxyl Emission; Infrared Astronomy; Interstellar Masers; Stellar Envelopes; Abundance; Dust; Gas Temperature; M Stars; Photodissociation; Stellar Mass Ejection; Water; Astrophysics full text sources ADS | data products SIMBAD (1)