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Nebular properties from far-infrared spectrosopyWe describe a semiempirical methodology-based on measurements of far-infrared (FIR) lines-that yields information on electron densities in regions where various ionic species exist, effective temperatures (T(sub eff)) for stars ionizing H II regions, and gas-phase heavy element abundances. Although this capability has long been available via optical data, the special features of FIR lines-relative insensitivity to extinction and electron temperature variations-extend the analysis ability. Several line ratios serve as diagnostics of electron density, N(sub e), probing different ionization conditions and different density regimes. The more N(sub e)-diagnostic observations made, the more reliable will be the deciphering of the actual variation in density throughout a nebula. A method to estimate T(sub eff) from the FIR (N III)/(N II) line ratio requires that the nebula be ionization bounded and that substantially all of the flux from the revevant lines be observed. However, to estimate T(sub eff) by a second method that uses the ratio of FIR (S III)/(O III) lines, an ionization-bounded nebula is a sufficient, but not necessary, condition. These restrictions are unnecessary for estimating densities and heavy element abundances. We show that a fairly general determination of metallicity, via the S/H ratio, may be made for H II regions with observations of just two lines-(S III) 19 micron and a hydrogen recombination line (or appropriate substitute). These techniques are applied to recent FIR data for the G333.6-0.2 H II region, including application to the recently measured (N II) 122 and 205 micron lines.
Document ID
19950040042
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Rubin, Robert H.
(SETI Enterprises, Moffett Field, CA United States)
Simpson, Janet P.
(Univ. of California, Berkeley, CA United States)
Lord, Steven D.
(IPAC, California Institute of Techology, CA United States)
Colgan, Sean W. J.
(SETI Enterprises, Moffett Field, CA United States)
Erickson, Edwin F.
(NASA Ames Research Center Moffett Field, CA, United States)
Haas, Michael R.
(NASA Ames Research Center Moffett Field, CA, United States)
Date Acquired
August 16, 2013
Publication Date
January 10, 1994
Publication Information
Publication: The Astrophysical Journal, Part 1
Volume: 420
Issue: 2
ISSN: 0004-637X
Subject Category
Astrophysics
Accession Number
95A71641
Distribution Limits
Public
Copyright
Other

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