Astronomy and Astrophysics – Astrophysics
Scientific paper
Nov 1982
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1982apj...262..189e&link_type=abstract
Astrophysical Journal, Part 1, vol. 262, Nov. 1, 1982, p. 189-197.
Astronomy and Astrophysics
Astrophysics
26
Interstellar Masers, Milky Way Galaxy, Orion Nebula, Carbon Monoxide, Hydrogen, Silicon Oxides, Stellar Mass Ejection, Water
Scientific paper
A model for the SiO maser radiation from Orion is constructed. The material around the source IRc2 is heated by turbulent motions. At a radius of nearly 100 trillion cm the temperature drops to about 1500 K, and dust grains begin to condense. Radiation pressure on the newly formed grains drives the material outward, leading to a mass loss rate of about 1/1000 solar mass/yr at a final velocity of 18 km/sec, provided the dust is underabundant by about factor 10. The maser turns on when the expansion velocity exceeds the mean turbulent velocity, so the nature of the velocity field changes from chaotic to ordered, and the required coherence can build up. Because the dust is optically thick, the SiO vibration transitions are exposed to an undiluted blackbody radiation field, and the only way to deviate from thermal equilibrium is for the gas to be warmer than the dust. This requirement can be obeyed for a rather limited set of parameters which may explain the uniqueness of Orion as the only star formation region displaying an SiO maser.
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