Physics
Scientific paper
Oct 1969
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1969pthph..42..781h&link_type=abstract
Progress of Theoretical Physics, Vol. 42, No. 4, pp. 781-798
Physics
50
Scientific paper
The evolution of gas clouds of masses, 104, 102 1 and 10-2 M&sun;, with the population I composition is investigated both for transparent and opaque stages by comparing the rates of cooling, heating, contraction and expansion. As heating and cooling processes in the transparent stage, we consider the thermal radiation from grains, the line-emission by H2, C+, Si+, C and O including the effect of self-absorption, the ionization of atoms by interstellar star-light and cosmic-ray particles, and the absorption of star-light by grains. In the opaque stage cooling is due to the diffusion of thermal photons. The results show that in the transparent stage a cloud much greater than 10-2 M&sun; contracts freely and cools down to about 10 °K if its mean density is greater than a certain critical value which depends on the mass of the cloud. In the opaque stage the cloud undergoes nearly adiabatic free-fall. On the other hand, if a cloud of mass nearly equal to or smaller than 1 × 10-2 M&sun; is formed with a mean density greater than a certain critical value, it establishes immediately gravitational equilibrium and the subsequent evolution is the Kelvin contraction.
Hattori Takeshi
Hayashi Chuichiro
Nakano Takanori
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