ARlogo Annu. Rev. Astron. Astrophys. 1999. 37:311-362
Copyright © 1999 by Annual Reviews. All rights reserved

Reprinted with kind permission from Annual Reviews, 4139 El Camino Way, Palo Alto, California, USA

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PHYSICAL CONDITIONS IN REGIONS OF STAR FORMATION

Neal J. Evans II


Department of Astronomy, The University of Texas at Austin


Abstract: The physical conditions in molecular clouds control the nature and rate of star formation, with consequences for planet formation and galaxy evolution. The focus of this review is on the conditions that characterize regions of star formation in our Galaxy. A review of the tools and tracers for probing physical conditions includes summaries of generally applicable results. Further discussion distinguishes between the formation of low-mass stars in relative isolation and formation in a clustered environment. Evolutionary scenarios and theoretical predictions are more developed for isolated star formation, and observational tests are beginning to interact strongly with the theory. Observers have identified dense cores collapsing to form individual stars or binaries, and analysis of some of these support theoretical models of collapse. Stars of both low and high mass form in clustered environments, but massive stars form almost exclusively in clusters. The theoretical understanding of such regions is considerably less developed, but observations are providing the ground rules within which theory must operate. The most rich and massive star clusters form in massive, dense, turbulent cores, which provide models for star formation in other galaxies.


Keywords: star formation, interstellar molecules, molecular clouds


Table of Contents

INTRODUCTION

PHYSICAL CONDITIONS

PROBES OF PHYSICAL CONDITIONS
Tracers of Column Density, Size, and Mass
Probes of Temperature and Density
Kinematics
Magnetic Field and Ionization
Observational and Analytical Tools

FORMATION OF ISOLATED LOW-MASS STARS
Theoretical Issues
Globules and Cores: Overall Properties
Globules and Cores: Internal Conditions
Classification of Sources and Evolutionary Scenarios
Detailed Theories
Tests of Evolutionary Hypotheses and Theory
Collapse
Summary of Isolated Star Formation

CLUSTERED STAR FORMATION AND MASSIVE STARS
Theoretical Issues
Overall Cloud and Core Properties
Evolutionary Scenarios and Detailed Theories
Filaments, Clumps, Gradients, and Disks
Kinematics
Implications for Larger Scales
Summary of Clustered Star Formation

CONCLUSIONS AND FUTURE PROSPECTS

REFERENCES

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