Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aas...209.8421n&link_type=abstract
2007 AAS/AAPT Joint Meeting, American Astronomical Society Meeting 209, #84.21; Bulletin of the American Astronomical Society, V
Astronomy and Astrophysics
Astrophysics
Scientific paper
HII regions form a complex matrix of gas and dust with the physical conditions being governed by the equation of state. Two fundamental issues in astrophysical research are the determination of physical conditions and chemical abundances in HII regions. Knowledge of chemical abundances is vital to the understanding of star formation, chemical evolution and nucleosynthesis. Collisionally excited strong line ratios address these two issues. For example, [SII] λ6716/ λ6731 is used to determine the electron density while R23 = (O[II] λ3727+ [OIII] λ4959,5007)/Hβ is used to determine the oxygen abundance. Strong line ratios have traditionally been studied as functions of ionization parameter and used as chemical abundance diagnostics. This simplistic approach cannot account for the diversity of observed strong line ratios. Recent authors, for example, have suggested that magnetic fields play an important role in the gas equation of state. We have developed a set of photoionization models in an attempt to provide a more complete picture by determining the effect of various physical conditions and geometry on the strong line ratios. In addition to magnetic field effects, we also consider the effects of dust by the inclusion of grains and PAHS which regulate the temperature and chemistry in the HII region complexes. Finally, we explore the effects of turbulence and the possible enhancement of local cosmic ray density due to compressed magnetic fields. We thank the National Science Foundation for its support through Ast 0607028.
Ferland Gary J.
Nemala Humeshkar B.
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