Astronomy and Astrophysics – Astrophysics
Scientific paper
May 1981
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1981a%26a....98..186h&link_type=abstract
Astronomy and Astrophysics, vol. 98, no. 1, May 1981, p. 186-194.
Astronomy and Astrophysics
Astrophysics
7
Atomic Energy Levels, Galactic Evolution, Gravitational Effects, Hydrogen Clouds, Radiative Heat Transfer, Stellar Evolution, Astronomical Models, Atomic Excitations, Collision Rates, Cosmology, Energy Dissipation, Multiphoton Absorption, Photoionization, Population Theory, Radiant Cooling, Thermodynamic Equilibrium
Scientific paper
Thermal evolution of a hydrogen gas cloud which contracts by self-gravitation in the pregalactic stage is investigated with regard to the change of level population of hydrogen atom and the growth of radiation field. It is found that collisional excitation of 1S-2S followed by two-photon decay works as the main loss mechanism of thermal energy. The gradual increase of ionization degree due to photoionization by two photons enhances the thermal energy loss rate so that the gas cloud contracts nearly isothermally at temperatures of approximately 6000-8000 K and enters the region where thermal energy exceeds radiation energy when thermal equilibrium between matter and radiation is achieved in the cloud. The subsequent evolution of the gas cloud is followed in consideration of energetics, and the mass range for the first-generation stars is estimated to be 0.1-20 solar masses.
Hasegawa Takuya
Sabano Yutaka
Yoshii Yoji
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