Journal
ASTROPHYSICAL JOURNAL
Volume 785, Issue 2, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/785/2/91
Keywords
atomic data; atomic processes; HII regions
Categories
Funding
- Division Of Astronomical Sciences
- Direct For Mathematical & Physical Scien [1313265] Funding Source: National Science Foundation
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The classic optical nebular diagnostics [NII], [OII], [OII], [SII], [SIII], and [ArIII] are employed to search for evidence of non-Maxwellian electron distributions, namely kappa distributions, in a sample of well-observed Galactic HII regions. By computing new effective collision strengths for all these systems and A-values when necessary (e. g., SII), and by comparing with previous collisional and radiative data sets, we have been able to obtain realistic estimates of the electron-temperature dispersion caused by the atomic data, which in most cases are not larger than similar to 10%. If the uncertainties due to both observation and atomic data are then taken into account, it is plausible to determine for some nebulae a representative average temperature while in others there are at least two plasma excitation regions. For the latter, it is found that the diagnostic temperature differences in the high-excitation region, e.g., T-e(OIII), Te(SIII), and Te(ArIII), cannot be conciliated by invoking kappa distributions. For the low-excitation region, it is possible in some, but not all, cases to arrive at a common, lower temperature for [NII], [OII], and [SII] with kappa approximate to 10, which would then lead to significant abundance enhancements for these ions. An analytic formula is proposed to generate accurate kappa-averaged excitation rate coefficients (better than 10% for kappa >= 5) from temperature tabulations of the Maxwell-Boltzmann effective collision strengths.
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