Energy levels, radiative rates and electron impact excitation rates for transitions in H-like N VII, O VIII, F IX, Ne X and Na XI

We report calculations of energy levels, radiative rates and electron impact excitation rates for transitions in H-like N VII, O VIII, F IX, Ne X and Na XI. The general-purpose relativistic atomic structure package (grasp) is adopted for calculating energy levels and radiative rates, while the Dirac atomic R-matrix code (DARC) and the flexible atomic code (FAC) are used for determining the collision strengths and subsequently the excitation rates. Oscillator strengths, radiative rates and line strengths are listed for all E1, E2, M1 and M2 transitions among the lowest 25 levels of the above five ions. Collision strengths have been averaged over a Maxwellian velocity distribution, and the effective collision strengths so obtained are reported over a wide temperature range below 10(7) K. Additionally, lifetimes are also given for all the calculated energy levels of the above five ions.

Energy levels, radiative rates and electron impact excitation rates for transitions in Li-like N V, F VII, Ne VIII and Na IX

In this paper, we report calculations of energy levels, radiative rates and electron impact excitation rates for transitions in Li-like N V, F VII, Ne VIII and Na IX. The general-purpose relativistic atomic structure package (GRASP) is adopted for calculating energy levels and radiative rates, while for determining the collision strengths and subsequently the excitation rates, the Dirac atomic R-matrix code (DARC) and the flexible atomic code (FAC) are used. Oscillator strengths, radiative rates and line strengths are reported for all E1, E2, M1 and M2 transitions among the lowest 24 levels of N V, F VII, Ne VIII and Na IX. Collision strengths have been averaged over a Maxwellian velocity distribution and the effective collision strengths so obtained are reported over a wide temperature range below 10(6.6) K. Additionally, lifetimes are also reported for all calculated levels of the above four ions.

X-ray and extreme-ultraviolet emission from the coronae of Capella

The primary objective of this work is the analysis and interpretation of coronal observations of Capella obtained in 1999 September with the High Energy Transmission Grating Spectrometer on the Chandra X-ray Observatory and the Extreme Ultraviolet Explorer (EUVE). He-like lines of O (O vii) are used to derive a density of 1.7 x 10(10) cm(-3) for the coronae of the binary, consistent with the upper limits derived from Fe xxi, Ne ix and Mg xi line ratios. Previous estimates of the electron density based on Fe xxi should be considered as upper limits. We construct emission measure distributions and compare the theoretical and observed spectra to conclude that the coronal material has a temperature distribution that peaks around 4-6 MK, implying that the coronae of Capella were significantly cooler than in the previous years. In addition, we present an extended line list with over 100 features in the 5-24 Angstrom wavelength range, and find that the X-ray spectrum is very similar to that of a solar flare observed with SMM. The observed to theoretical Fe xvii 15.012-Angstrom line intensity reveals that opacity has no significant effect on the line flux. We derive an upper limit to the optical depth, which we combine with the electron density to derive an upper limit of 3000 km for the size of the Fe xvii emitting region. In the same context, we use the Si iv transition region lines of Capella from HST/Goddard High-Resolution Spectrometer observations to show that opacity can be significant at T = 10(5) K, and derive a path-length of approximate to 75 kin for the transition region. Both the coronal and transition region observations are consistent with very small emitting regions, which could be explained by small loops over the stellar surfaces.