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Title:
The Formation of the First Stars. II. Radiative Feedback Processes and Implications for the Initial Mass Function
Authors:
McKee, Christopher F.; Tan, Jonathan C.
Affiliation:
AA(Departments of Physics and Astronomy, University of California, Berkeley, CA 94720; .), AB(Department of Astronomy, University of Florida, Gainesville, FL 32611; .)
Publication:
The Astrophysical Journal, Volume 681, Issue 2, pp. 771-797. (ApJ Homepage)
Publication Date:
07/2008
Origin:
UCP
ApJ Keywords:
Cosmology: Theory, Cosmology: Early Universe, Stars: Formation
Abstract Copyright:
(c) 2008: The American Astronomical Society
DOI:
10.1086/587434
Bibliographic Code:
2008ApJ...681..771M

Abstract

We consider the radiative feedback processes that operate during the formation of the first stars. (1) Photodissociation of H2 in the local dark matter minihalo occurs early in the growth of the protostar but does not affect subsequent accretion. (2) Lyα radiation pressure acting at the boundary of the H II region that the protostar creates in the accreting envelope reverses infall in the polar directions when the star reaches ~20-30 Msolar but cannot prevent infall from other directions. (3) Expansion of the H II region beyond the gravitational escape radius for ionized gas occurs at masses ~50-100 Msolar. However, accretion from the equatorial regions can continue since the neutral accretion disk shields a substantial fraction of the accretion envelope from direct ionizing flux. (4) At higher stellar masses, ~140 Msolar in the fiducial case, photoevaporation-driven mass loss from the disk, together with declining accretion rates, halts the increase in the protostellar mass. We identify this process as the mechanism that determines the mass of Population III.1 stars (i.e., stars with primordial composition that have not been affected by prior star formation). The initial mass function of these stars is set by the distribution of entropy and angular momentum. The Appendix gives approximate solutions to a number of problems relevant to the formation of the first stars: the effect of Rayleigh scattering on line profiles in media of very large optical depth, the intensity of Lyα radiation in very opaque media, radiative acceleration in terms of the gradient of a modified radiation pressure, the flux of radiation in a shell with an arbitrary distribution of opacity, and the vertical structure of an accretion disk supported by gas pressure with constant opacity.
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