Electron impact excitation of Ar XVII

Energies for the lowest 49 levels among the 1s(2) and 1snl (n = 2-5) configurations of Ar XVII have been calculated using the GRASP code of Dyall et al. (1989, Comput. Phys. Comm., 55, 424). 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 among these levels. Furthermore, collision strengths have also been calculated for all the 1176 transitions among the above 49 levels using the Dirac Atomic R-matrix Code (DARC) of Norrington & Grant (2005, Comput. Phys. Commun., in preparation), over a wide energy range up to 580 Ryd. Resonances have been resolved in the threshold region, and effective collision strengths have been obtained over a wide temperature range up to log T-e = 7.2 K. Comparisons are made with the limited results available in the literature, and the accuracy of the data is assessed. Our energy levels are estimated to be accurate to better than 0.1%, whereas results for other parameters are probably accurate to better than 20%.

Radiative rates for E1, E2, M1 and M2 transitions in Fe X

Energies of the 54 levels belonging to the (1s(2)2s(2)2p(6)) 3s(2)3p(5), 3s3p(6), 3s(2)3p(4)3d and 3s3p(5)3d configurations of Fe X have been calculated using the GRASP code of Dyall et al. (1989). 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 among these levels. Comparisons are made with results available in the literature, and the accuracy of the data is assessed. Our energy levels are estimated to be accurate to better than 3%, whereas results for other parameters are probably accurate to better than 20%. Additionally, the agreement between measured and calculated lifetimes is better than 10%.

Electron impact excitation of Fe XIII

Energy levels and radiative rates for transitions among the lowest 97 fine-structure levels belonging to the (1s(2) 2s(2) 2p(6)) 3 s(2) 3p(2), 3s3p(3), 3s(2) 3p3d, 3p(4), 3s3p(2) 3d and 3s(2) 3d(2) configurations of Fe XIII have been calculated using the fully relativistic GRASP code. Additionally, collision strengths for transitions among these levels have been computed using the Dirac Atomic R-matrix Code (DARC) of Norrington & Grant (2004). Radiative rates and oscillator strengths are tabulated for all allowed transitions among the 97 fine-structure levels, while collision strengths are reported for some transitions at a few energies above thresholds. Comparisons are made with the available results, and the accuracy of the data is assessed.

Excitation rates for transitions in Ca XV

Collision strengths for transitions among the energetically lowest 46 fine-structure levels belonging to the (1s(2)) 2s(2)2p(2), 2s2p(3), 2p(4), and 2s(2)2p3l configurations of Ca XV are computed, over a wide electron energy range below 300 Ryd, using the Dirac Atomic R-matrix Code (DARC) of Norrington & Grant (2003). Resonances in the threshold region have been resolved in a fine energy mesh, and excitation rates are determined over a wide electron temperature range below 10(7) K. The results are compared with those available in the literature, and the accuracy of the data is assessed.

Effective collision strengths for transitions in Fe XI

Collision strengths for transitions among the lowest 48 fine- structure levels belonging to the (1s(2)2s(2)2p(6)) 3s(2)3p(4), 3s3p(5), 3s(2)3p(3)3d and 3p(6) configurations of Fe XI have been calculated using the Dirac Atomic R-matrix Code (DARC) of Norrington & Grant (2003). Results are tabulated at energies above thresholds in the range 10 less than or equal to E less than or equal to 100 Ry, although resonances have been resolved in a fine energy mesh in the thresholds region. Effective collision strengths, obtained after integrating the collision strengths over a Maxwellian distribution of electron velocities, are also tabulated over a wide electron temperature range below 5 x 10(6) K. Comparisons with other available results are made, and the accuracy of the present data is assessed.

Radiative rates for transitions in Fe XVII

Energies of the lowest 157 levels belonging to the (1s(2)) 2s(2)2p(6), 2s(2)p(5)3l, 2s(2)2p(5)4l, 2s(2)2p(5)4l, 2s2p(5)5l, 2s2p(6)4l and 2s2p(6)5l configurations of Fe XVII have been calculated using the GRASP code of Dyall et al. (1989). Additionally, radiative rates, oscillator strengths, and line strengths are calculated for all electric dipole (E I), magnetic dipole (M I), electric quadrupole (E2), and magnetic quadrupole (M2) transitions among these levels. Comparisons are made with the results already available in the literature, and the accuracy of the data is assessed. Our energy levels are expected to be accurate to better than M whereas results for other parameters are probably accurate to better than 20%.

Effective collision strengths for transitions in Fe XV

Collision strengths for transitions among the energetically lowest 53 fine-structure levels belonging to the (1s(2)2s(2)2p(6)) 3l(2), 3l3l', 3s4l and 3p4s configurations of Fe XV are computed, over an electron energy range below 160 Ryd, using the Dirac Atomic R-matrix Code (DARC) of Norrington & Grant (2003). Effective collision strengths, obtained after integrating the collision strengths over a Maxwellian distribution of electron energies, have also been calculated. These results of effective collision strengths are tabulated for all 1378 inelastic transitions over a wide temperature range of 10(5) to 10(7) K. Comparisons are also made with other R-matrix calculations and the accuracy of the results is assessed.

Oscillator strengths for transitions in C-like ions between K XIV and Mn XX

Energy levels and oscillator strengths (transition probabilities) have been calculated for transitions among 46 fine-structure levels of the (1s(2)) 2s(2) 2p(2), 2s2p(3),2p(4), 2s(2)2p3s, 2s(2) 2p3p and 2s(2)2p3d configurations of C-like K XIV, Sc XVI, Ti XVII, V XVIII, Cr XIX and Mn XX using the GRASP code. Configuration interaction and relativistic effects have been included while generating the wavefunctions. Calculated values of energy levels agree within 3% with the experimentally compiled results, and the length and velocity forms of oscillator strengths agree within 20% for a majority of allowed transitions.

Energy levels, radiative rates, and collision strengths for transitions in Fe XVII

Energy levels and radiative rates have been calculated for fine-structure transitions among the lowest 89 levels of the (1s(2)) 2s(2)2p(6), 2s(2) 2p(5) 3 l, 2s(2) 2p(5) 4l, 2s2p(6) 3 l, and 2s2p(6)4l configurations of Fe XVII using the GRASP code of Dyall et al. Collision strengths have also been calculated, for transitions among the lowest 55 levels, using the recently developed Dirac atomic R-matrix code (DARC) of Norrington & Grant. The results are compared with those available in the literature, and the accuracy of the data is assessed.

Energy levels and radiative rates for transitions in Ar XIII, Ar XIV and Ar XV

Energies for 524 levels of Ar XIII, 460 levels of Ar XIV and 156 levels of Ar XV have been calculated using the GRASP code of Dyall et al. (1989). 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 among these levels. Comparisons are made with the limited results available in the literature, and the accuracy of the data is assessed. Our energy levels are estimated to be accurate to better than 1%, whereas results for other parameters are probably accurate to better than 20%. Additionally, the level lifetimes derived from our radiative rates are in excellent agreement with measured values.

Opacity in the upper atmosphere of AU Mic

In this paper we investigate the validity of the optically thin assumption in the transition region of the late-type star AU Mic. We use Far-Ultraviolet Spectroscopic Explorer (FUSE) observations of the C III multiplet and O VI resonance lines, hence yielding information at two different levels within the atmosphere. Significant deviations from the optically thin fluxes are found for C III in both quiescent and flare spectra, where only 60% of the flux is actually observed. This could explain the apparent deviation of C III observed in emission measure distributions. We utilize escape probabilities for both homogeneous and inhomogeneous geometries and calculate optical depths as high as 10 for the C III 1175.71 Angstrom component of the multiplet. Using a lower limit to the electron density (10(11) cm(-3))we derive an effective thickness of

Wavelet phase coherence analysis: Application to a quiet-sun magnetic element

A new application of wavelet analysis is presented that utilizes the inherent phase information residing within the complex Morlet transform. The technique is applied to a weak solar magnetic network region, and the temporal variation of phase difference between TRACE 1700 Angstrom and SOHO/SUMER C II 1037 Angstrom intensities is shown. We present, for the first time in an astrophysical setting, the application of wavelet phase coherence, including a comparison between two methods of testing real wavelet phase coherence against that of noise. The example highlights the advantage of wavelet analysis over more classical techniques, such as Fourier analysis, and the effectiveness of the former to identify wave packets of similar frequencies but with differing phase relations is emphasized. Using cotemporal, ground-based Advanced Stokes Polarimeter measurements, changes in the observed phase differences are shown to result from alterations in the magnetic topology.

A detailed study of opacity in the upper atmosphere of Proxima Centauri

We present far-UV and UV spectroscopic observations of Proxima Centauri obtained as part of our continued investigation into the optically thin approximation assumed for the transition regions of late-type stars. Significant opacity is found in the C III lines during both the quiescent and flaring states of Proxima Cen, with up to 70% of the expected flux being lost in the latter. Our findings cast some doubt on the suitability of the C III lambda977 line for estimating the electron density in stellar atmospheres. However, the opacity has no significant effect on the observed line widths. We calculate optical depths for homogeneous and inhomogeneous geometries and estimate an electron density of 6 x 10(10) cm(-3) for the transition region using the O IV line ratios at 1400 Angstrom. The combination of electron density and optical depth indicates path lengths as low as approximate to 10 km, which are in excellent agreement with estimates of the small-scale structure seen in the solar transition region.

The extreme-ultraviolet structure and properties of a newly emerged active region

The structure and properties of a newly emerged solar active region (NOAA Active Region 7985) are discussed using the Coronal Diagnostic Spectrometer (CDS) and the Extreme- Ultraviolet Imaging Telescope (EIT) on board the Solar and Heliospheric Observatory. CDS obtained high-resolution EUV spectra in the 308-381 Angstrom and 513-633 Angstrom wavelength ranges, while EIT recorded full-disk EUV images in the He II (304 Angstrom), Fe IX/X (171 Angstrom), Fe xii (195 Angstrom), and Fe XV (284 Angstrom) bandpasses. Electron density measurements from Si rx, Si X, Fe xii, Fe XIII, and Fe xiv line ratios indicate that the region consists of a central high- density core with peak densities of the order of 1.2 x 10(10) cm(-3), which decrease monotonically to similar to5.0 X 10(8) cm(-3) at the active region boundary. The derived electron densities also vary systematically with temperature. Electron pressures as a function of both active region position and temperature were estimated using the derived electron densities and ion formation temperatures, and the constant pressure assumption was found to be an unrealistic simplification. Indeed, the active region is found to have a high-pressure core (1.3 x 10(16) cm(-3) K) that falls to 6.0 x 10(14) cm(-3) K just outside the region. CDS line ratios from different ionization stages of iron, specifically Fe xvi (335.4 Angstrom) and Fe xiv (334.4 Angstrom), were used to diagnose plasma temperatures within the active region. Using this method, peak temperatures of 2.1 x 10(6) K were identified. This is in good agreement with electron temperatures derived using EIT filter ratios and the two-temperature model of Zhang et al. The high- temperature emission is confined to the active region core, while emission from cooler (1-1.6) x 10(6) K lines originates in a system of loops visible in EIT 171 and 195 X images. Finally, the three-dimensional geometry of the active region is investigated using potential field extrapolations from a Kitt Peak magnetogram. The combination of EUV and magnetic field extrapolations extends the "core-halo" picture of active region structure to one in which the core is composed of a number of compact coronal loops that confine the hot, dense, high- pressure core plasma while the halo emission emerges from a system of cooler and more extended loops.

Energy levels and transition probabilities for nitrogen-like Fe xx

Energies of the 700 lowest levels in Fe XX have been obtained using the multiconfiguration Dirac-Fock method. Configuration interaction method on the basis set of transformed radial orbitals with variable parameters taking into account relativistic corrections in the Breit-Pauli approximation was used to crosscheck our presented results. Transition probabilities, oscillator and line strengths are presented for electric dipole (E1), electric quadrupole (E2) and magnetic dipole (M1) transitions among these levels. The total radiative transition probabilities from each level are also provided. Results are compared with data compiled by NIST and with other theoretical work.