Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userFine structure collision strengths and line ratios for [Ne V] in infrared and optical sources
154
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Improved collisions strengths for the mid-infrared and optical transitions in Ne V are presented. Breit-Pauli R-Matrix calculations for electron impact excitation are carried out with fully resolved near-threshold resonances at very low energies. In particular, the fine structure lines at 14 micron and 24 micron due to transitions among the ground state levels 1s^22s^22p^3 (^3P_{0,1,2}), and the optical/near-UV lines at 2973, 3346 and 3426 Angstrom transitions among the ^3P_{0,1,2}, ^1D_2, ^1S_0 levels are described. Maxwellian averaged collision strengths are tabulated for all forbidden transistion within the ground configuration. Significant differences are found in the low temperature range Te < 10000 K for both the FIR and the opitcal transitions compared to previous results. An analysis of the 14/24 line ratio in low-energy-density (LED) plasma conditions reveals considerable variation; the effective rate coefficient may be dominated by the very low-energy behaviour rather than the maxwellian averaged collision strengths. Computed values suggest a possible solution to the anomalous mid-IR ratios found to be lower than theoretical limits observed from planetary nebulae and Seyfert galaxies. While such LED conditions may be present in infrared sources, they might be inconsistent with photoionization equilibrium models.
rate research
Read More
We present electron collision strengths and their thermally averaged values for the forbidden lines of the astronomically abundant doubly-ionized oxygen ion, O^{2+}, in an intermediate coupling scheme using the Breit-Pauli relativistic terms as implemented in an R-matrix atomic scattering code. We use several atomic targets for the R-matrix scattering calculations including one with 72 atomic terms. We also compare with new results obtained using the intermediate coupling frame transformation method. We find spectroscopically significant differences against a recent Breit-Pauli calculation for the excitation of the [O III] lambda 4363 transition but confirm the results of earlier calculations.
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.
We present effective collision strengths for electron excitation and de-excitation of the ten forbidden transitions between the five lowest energy levels of the astronomically abundant doubly-ionised oxygen ion, O^{2+}. The raw collision strength data were obtained from an R-matrix intermediate coupling calculation using the Breit-Pauli relativistic approximation published previously by the authors. The effective collision strengths were calculated with kappa-distributed electron energies and are tabulated as a function of the electron temperature and kappa.
We present Maxwellian-averaged effective collision strengths for the electron-impact excitation of S III over a wide range of electron temperatures of astrophysical importance, log T(K) = 3.0-6.0. The calculation incorporates 53 fine-structure levels arising from the six lowest configurations, giving rise to 1378 individual lines, and is undertaken using the recently developed RMATRX II plus FINE95 suite of codes. A detailed comparison is made with a previous R-matrix calculation and significant differences are found for some transitions. The atomic data are subsequently incorporated into the modeling code CLOUDY to generate line intensities for a range of plasma parameters, with emphasis on allowed UV and EUV emission lines detected from the Io plasma torus. Electron density-sensitive line ratios are calculated with the present atomic data and compared with those from CHIANTI v7.1, as well as with Io plasma torus spectra obtained by FUSE and EUVE. The present line intensities are found to agree well with the observational results and provide a noticeable improvement upon the values predicted by CHIANTI.
We present Herschel observations of six fine-structure lines in 25 Ultraluminous Infrared Galaxies at z<0.27. The lines, [O III]52, [N III]57, [O I]63, [N II]122, [O I]145, and [C II]158, are mostly single gaussians with widths <600 km s-1 and luminosities of 10^7 - 10^9 Solar. There are deficits in the [O I]63/L_IR, [N II]/L_IR, [O I]145/L_IR, and [C II]/L_IR ratios compared to lower luminosity systems. The majority of the line deficits are consistent with dustier H II regions, but part of the [C II] deficit may arise from an additional mechanism, plausibly charged dust grains. This is consistent with some of the [C II] originating from PDRs or the ISM. We derive relations between far-IR line luminosities and both IR luminosity and star formation rate. We find that [N II] and both [O I] lines are good tracers of IR luminosity and star formation rate. In contrast, [C II] is a poor tracer of IR luminosity and star formation rate, and does not improve as a tracer of either quantity if the [C II] deficit is accounted for. The continuum luminosity densities also correlate with IR luminosity and star formation rate. We derive ranges for the gas density and ultraviolet radiation intensity of 10^1 < n < 10^2.5 and 10^2.2 < G_0 < 10^3.6, respectively. These ranges depend on optical type, the importance of star formation, and merger stage. We do not find relationships between far-IR line properties and several other parameters; AGN activity, merger stage, mid-IR excitation, and SMBH mass. We conclude that these far-IR lines arise from gas heated by starlight, and that they are not strongly influenced by AGN activity.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
