Carbon depletion in turbulent molecular cloud cores

Details Carbon depletion in turbulent molecular cloud cores Carbon depletion in turbulent molecular cloud cores

Oct 1982

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1982apj...261..110b&link_type=abstract

Astrophysical Journal, Part 1, vol. 261, Oct. 1, 1982, p. 110-114. Research supported by the Netherlands Foundation for Astrono

Astronomy and Astrophysics

Astrophysics

87

Abundance, Carbon, Interstellar Gas, Molecular Clouds, Turbulence Effects, Depletion, Molecular Collisions

Scientific paper

Observations of dense molecular cores indicate that about 10% of the carbon is still in the gas phase (depletion factor of about 0.1) in spite of the fact that the depletion time - the time needed for heavy elements to freeze out on dust grains - is several orders of magnitude smaller than the cloud lifetime. To resolve this problem, it is suggested that the material in molecular cloud cores is circulated by turbulence and that every time a parcel of gas and dust reaches the outer layers of the core, dust mantles that have formed by accretion in the center are evaporated and/or photodesorbed. The observed mild degree of depletion results because the circulation time and the depletion time are of the same order of magnitude. Since the time to reach molecular equilibrium in the outer layers of a cloud core is short compared with the circulation time the dust plays no role in the chemistry. In the center of a cloud core, the time to convert C to CO is of the order of the circulation time, so that an appreciable fraction of the gaseous carbon remains in atomic form. From a brief discussion of the energetics, it is concluded that the turbulence observed in molecular cloud cores can be maintained during the lifetime of the cloud if the envelope collapses onto the core at a rate of about 0.000001 solar mass per year.

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