Measuring nebular temperatures: the effect of new collision strengths with equilibrium and kappa-distributed electron energies

In this paper we develop tools for observers to use when analysing nebular spectra for temperatures and metallicities, with two goals: to present a new, simple method to calculate equilibrium electron temperatures for collisionally excited line flux ratios, using the latest atomic data; and to adapt current methods to include the effects of possible non-equilibrium '{\kappa}' electron energy distributions. Adopting recent collision strength data for [O iii], [S iii], [O ii], [S ii], and [N ii], we find that existing methods based on older atomic data seriously overestimate the electron temperatures, even when considering purely Maxwellian statistics. If {\kappa} distributions exist in H ii regions and planetary nebulae as they do in solar system plasmas, it is important to investigate the observational consequences. This paper continues our previous work on the {\kappa} distribution (Nicholls et al. 2012). We present simple formulaic methods that allow observers to (a) measure equilibrium electron temperatures and atomic abundances using the latest atomic data, and (b) to apply simple corrections to existing equilibrium analysis techniques to allow for possible non-equilibrium effects. These tools should lead to better consistency in temperature and abundance measurements, and a clearer understanding of the physics of H ii regions and planetary nebulae.Comment: 15 figures. Accepted for publication in ApJ

Improved collision strengths and line ratios for forbidden [O III] far-infrared and optical lines

Far-infrared and optical [O III] lines are useful temeprature-density diagnostics of nebular as well as dust obscured astrophysical sources. Fine structure transitions among the ground state levels 1s^22s^22p^3 \ ^3P_{0,1,2} give rise to the 52 and 88 micron lines, whereas transitions among the $^3P_{0,1,2}, ,^1D_2, ^1S_0$ levels yield the well-known optical lines 4363, 4959 and 5007 Angstroms. These lines are excited primarily by electron impact excitation. But despite their importance in nebular diagnostics collision strengths for the associated fine structure transitions have not been computed taking full account of relativistic effects. We present Breit-Pauli R-matrix calculations for the collision strengths with highly resolved resonance structures. We find significant differences of up to 20% in the Maxwellian averaged rate coefficients from previous works. We also tabulate these to lower temperatures down to 100 K to enable determination of physical conditions in cold dusty environments such photo-dissociation regions and ultra-luminous infrared galaxies observed with the Herschel space observatory. We also examine the effect of improved collision strengths on temperature and density sensitive line ratios.Comment: Letter in press, Monthly Notices of Royal Astronomical Society, 5 pages, 6 figure

Muddy Waters: Congressional Consent and the Great Lakes - St. Lawrence River Basin Water Resources Compact

After nearly a century of negotiations among the Great Lakes states, tribes, and provinces, a promising new agreement was recently ratified by the parties and recognized by Congress, this is the Great Lakes-St. Lawrence River Basin Water Resources Compact. Interstate compacts, may serve as a particularly useful tool for solving regional environmental problems, which the federal government lacks the interest to resolve. However, due to constitutional strictures, interstate compacts are not binding unless Congress grants consent to the compact. This Note focuses on the recent Great Lakes Compact as a means to examine the current state of the law surrounding the Compact Clause of the United States Constitution. The author argues that while compacting states have a myriad of arguments at their disposal that Congress has impliedly consented to a compact, the most prudent path is to have Congress formally adopt the compact as federal law by explicitly consenting to it. In coming to this conclusion, the Note examines the history of the Compact Clause of the Constitution as well as prior attempt by the Great Lakes states to enter into agreements