Energy levels, radiative rates and electron impact excitation rates for transitions in He-like Ga XXX, Ge XXXI, As XXXII, Se XXXIII and Br XXXIV

We report calculations of energy levels, radiative rates and electron impact excitation cross sections and rates for transitions in He-like Ga XXX, Ge XXXI, As XXXII, Se XXXIII and Br XXXIV. The {\sc grasp} (general-purpose relativistic atomic structure package) is adopted for calculating energy levels and radiative rates. For determining the collision strengths, and subsequently the excitation rates, the Dirac Atomic R-matrix Code ({\sc darc}) is used. Oscillator strengths, radiative rates and line strengths are reported for all E1, E2, M1 and M2 transitions among the lowest 49 levels of each ion. Additionally, theoretical lifetimes are provided for all 49 levels of the above five ions. Collision strengths are averaged over a Maxwellian velocity distribution and the effective collision strengths obtained listed over a wide temperature range up to 10$^{8}$ K. Comparisons are made with similar data obtained using the Flexible Atomic Code ({\sc fac}) to highlight the importance of resonances, included in calculations with {\sc darc}, in the determination of effective collision strengths. Discrepancies between the collision strengths from {\sc darc} and {\sc fac}, particularly for some forbidden transitions, are also discussed. Finally, discrepancies between the present results for effective collision strengths with the {\sc darc} code and earlier semi-relativistic $R$-matrix data are noted over a wide range of electron temperatures for many transitions in all ions.Comment: 11 pages of Text, 11 Figures and 4 Tables. Ref: Physica Scripta 87 (2013) in press. arXiv admin note: substantial text overlap with arXiv:1207.6525, arXiv:1209.2914, arXiv:1207.542

Ultraviolet emission lines of Si II in quasars --- investigating the "Si II disaster"

The observed line intensity ratios of the Si II 1263 and 1307 \AA\ multiplets to that of Si II 1814\,\AA\ in the broad line region of quasars are both an order of magnitude larger than the theoretical values. This was first pointed out by Baldwin et al. (1996), who termed it the "Si II disaster", and it has remained unresolved. We investigate the problem in the light of newly-published atomic data for Si II. Specifically, we perform broad line region calculations using several different atomic datasets within the CLOUDY modeling code under optically thick quasar cloud conditions. In addition, we test for selective pumping by the source photons or intrinsic galactic reddening as possible causes for the discrepancy, and also consider blending with other species. However, we find that none of the options investigated resolves the Si II disaster, with the potential exception of microturbulent velocity broadening and line blending. We find that a larger microturbulent velocity ($\sim 500 \rm \, kms^{-1}$) may solve the Si II disaster through continuum pumping and other effects. The CLOUDY models indicate strong blending of the Si II 1307 \AA\ multiplet with emission lines of O I, although the predicted degree of blending is incompatible with the observed 1263/1307 intensity ratios. Clearly, more work is required on the quasar modelling of not just the Si II lines but also nearby transitions (in particular those of O I) to fully investigate if blending may be responsible for the Si II disaster.Comment: Accepted for publication in Ap

Electron Impact Excitation of S III: An Assessment

In a recent paper, Tayal et al. (Astrophys. J. Suppl. 2019, 242, 9) reported results for energy levels, radiative rates (A-values), and effective collision strengths ( Υ ) for transitions among the 198 levels of Si-like S III. For the calculations, they adopted the multi-configuration Hartree–Fock (MCHF) code for the energy levels and A-values and the B-spline R-matrix (BSR) code for Υ . Their reported results appear to be accurate for energy levels and A-values, but not for Υ . Through our independent calculations by adopting the flexible atomic code (FAC), we demonstrate that their reported results for Υ are underestimated, by up to a factor of two, and at all temperatures, particularly for the allowed transitions, but some forbidden ones as well. Additionally, for transitions involving the higher levels, the behaviour of their Υ results is not correct

Energy levels, radiative rates and electron impact excitation rates for transitions in Be-like Cl XIV, K XVI and Ge XXIX

Results for energy levels, radiative rates and electron impact excitation (effective) collision strengths for transitions in Be-like Cl XIV, K XVI and Ge XXIX are reported. For the calculations of energy levels and radiative rates the general-purpose relativistic atomic structure package is adopted, while for determining the collision strengths and subsequently the excitation rates, the Dirac atomic R-matrix code is used. Oscillator strengths, radiative rates and line strengths are listed for all E1, E2, M1 and M2 transitions among the lowest 98 levels of the n ≤ 4 configurations. Furthermore, lifetimes are provided for all levels and comparisons made with available theoretical and experimental results. Resonances in the collision strengths are resolved in a fine energy mesh and averaged over a Maxwellian velocity distribution to obtain the effective collision strengths. Results obtained are listed over a wide temperature range up to 107.8 K, depending on the ion.</p

Electron impact excitation of Be-like ions: a comparison of DARC and ICFT results

Emission lines of Be-like ions are frequently observed in astrophysical plasmas, and many are useful for density and temperature diagnostics. However, accurate atomic data for energy levels, radiative rates (A-values) and effective electron excitation collision strengths ($\Upsilon$) are required for reliable plasma modelling. In general it is reasonably straightforward to calculate energy levels and A- values to a high level of accuracy. By contrast, considerable effort is required to calculate $\Upsilon$, and hence it is not always possible to assess the accuracy of available data. Recently, two independent calculations (adopting the $R$-matrix method) but with different approaches (DARC and ICFT) have appeared for a range of Be-like ions. Therefore, in this work we compare the two sets of $\Upsilon$, highlight the large discrepancies for a significant number of transitions and suggest possible reasons for these.Comment: 9 pages including 2 figures, will appear in 2015 MNRA

MODEL SUSCEPTIBLE EXPOSED INFECTED RECOVERED (SEIR) DENGAN IMIGRASI

Energies and lifetimes are reported for the lowest 136 levels of Fe XIV, belonging to the (1s$^2$2s$^2$2p$^6$) 3s$^2$3p, 3s3p$^2$, 3s$^2$3d, 3p$^3$, 3s3p3d, 3p$^2$3d, 3s3d$^2$, 3p3d$^2$ and 3s$^24\ell$ configurations. Additionally, radiative rates, oscillator strengths and line strengths are calculated for all electric dipole (E1), magnetic dipole (M1), electric quadrupole (E2) and magnetic quadrupole (M2) transitions. Theoretical lifetimes determined from these radiative rates for most levels show satisfactory agreement with earlier calculations, as well as with measurements. Electron impact excitation collision strengths are also calculated with the Dirac atomic $R$-matrix code (DARC) over a wide energy range up to 260 Ryd. Furthermore, resonances have been resolved in a fine energy mesh to determine effective collision strengths, obtained after integrating the collision strengths over a Maxwellian distribution of electron velocities. Results are listed for all 9180 transitions among the 136 levels over a wide range of electron temperatures, up to 10$^{7.1}$ K. Comparisons are made with available results in the literature, and the accuracy of the present data is assessed.Comment: Text including figures and tables: 17 p, figures: 5, tables: 8, will be published in MNRAS (2014