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Cold Atomic Hydrogen, Narrow Self-Absorption, and the Age of Molecular CloudsThis viewgraph presentation reviews the history, and current work on HI and its importance in star formation. Through many observations of HI Narrow Self Absorption (HINSA) the conclusions are drawn and presented. Local molecular clouds have HI well-mixed with molecular constituents This HI is cold, quiescent, and must be well-shielded from the UV radiation field The density and fractional abundance (wrt H2) of the cold HI are close to steady state values The time required to convert these starless clouds from purely HI initial state to observed present composition is a few to ten million years This timescale is a lower limit - if dense clouds being swept up from lower density regions by shocks, the time to accumulate material to get A(sub v) is approximately 1 and provide required shielding may be comparable or longer
Document ID
Document Type
Conference Paper
External Source(s)
Goldsmith, Paul F.
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Date Acquired
August 24, 2013
Publication Date
May 22, 2006
Subject Category
Meeting Information
Meeting: Scientific Colloquium at Istitut de Radioastronomie Millimetrique (IRAM)
Location: Grenoble
Country: France
Start Date: May 22, 2006
Distribution Limits
star formation
atomic hydrogen
time scale
molecular clouds

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