2014/02/28 by C. Mendoza, M. A. Bautista
Physics and Astronomy · #Collision #Collisional excitation #Dispersion (optics) #Dust and Plasma Wave Phenomena #Electron #Electron temperature #Excitation #Ionosphere and magnetosphere dynamics #Plasma #Radiative transfer #Solar and Space Plasma Dynamics #astro-ph.IM #astro-ph.SR
paper · pdf · doi:10.1088/0004-637x/785/2/91
44 pages, 9 figures, accepted for publication in the Astrophysical Journal
arxiv created 2014/03/07 · openalex publication_date 2014/03/31 · arxiv updated 2015/06/18 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
The classic optical nebular diagnostics [N ii ], [O ii ], [O iii ], [S ii ], [S iii ], and [Ar iii ] are employed to search for evidence of non-Maxwellian electron distributions, namely κ distributions, in a sample of well-observed Galactic H ii regions. By computing new effective collision strengths for all these systems and A -values when necessary (e.g., S ii ), 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 ∼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 (O iii ), T e (S iii ), and T e (Ar iii ), cannot be conciliated by invoking κ distributions. For the low-excitation region, it is possible in some, but not all, cases to arrive at a common, lower temperature for [N ii ], [O ii ], and [S ii ] with κ ≈ 10, which would then lead to significant abundance enhancements for these ions. An analytic formula is proposed to generate accurate κ-averaged excitation rate coefficients (better than 10% for κ ⩾ 5) from temperature tabulations of the Maxwell–Boltzmann effective collision strengths.