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Title: Photoionization of Ca XV with high energy features

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Journal Article: Publisher's Accepted Manuscript
Journal Name:
New Astronomy
Additional Journal Information:
Journal Volume: 51; Journal Issue: C; Related Information: CHORUS Timestamp: 2017-10-04 16:31:35; Journal ID: ISSN 1384-1076
Country of Publication:
Country unknown/Code not available

Citation Formats

Nahar, Sultana N. Photoionization of Ca XV with high energy features. Country unknown/Code not available: N. p., 2017. Web. doi:10.1016/j.newast.2016.08.010.
Nahar, Sultana N. Photoionization of Ca XV with high energy features. Country unknown/Code not available. doi:10.1016/j.newast.2016.08.010.
Nahar, Sultana N. Wed . "Photoionization of Ca XV with high energy features". Country unknown/Code not available. doi:10.1016/j.newast.2016.08.010.
title = {Photoionization of Ca XV with high energy features},
author = {Nahar, Sultana N.},
abstractNote = {},
doi = {10.1016/j.newast.2016.08.010},
journal = {New Astronomy},
number = C,
volume = 51,
place = {Country unknown/Code not available},
year = {Wed Feb 01 00:00:00 EST 2017},
month = {Wed Feb 01 00:00:00 EST 2017}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1016/j.newast.2016.08.010

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  • We present relativistic close-coupling photoionization calculations of Ni XV using the Breit-Pauli R-matrix method to obtain photoionization cross section of Ni XV from the ground state 3s {sup 2}3p {sup 2}({sup 3} P {sub 0}) and the lowest four 3s {sup 2}3p {sup 2} ({sup 3} P {sub 1,2}, {sup 1} D {sub 2}, {sup 1} S {sub 0}) excited states. A multiconfiguration eigenfunction expansion of the core Ni XVI is employed with configurations 3s {sup 2}3p, 3s3p {sup 2}, 3s {sup 2}3d, 3p {sup 3}, 3s3p3d, 3p {sup 2}3d, 3s3d {sup 2}, 3p3d {sup 2}. We have included themore » lowest 40 target level states of Ni XVI in the photoionization calculations of Ni XV. Cross sections are determined by the Rydberg series of autoionizing resonances converging to several ionic states of Ni XVI. In our calculations, we have taken into account all the important physical effects such as exchange, channel coupling, and short-range correlation. Further, relativistic effects are incorporated by including mass correction, Darwin term, and spin-orbit interaction terms. The present calculations using the lowest 40 target levels of Ni XVI are presented for the first time and can be useful for modeling the ionization balance of Ni XV in laboratory and astrophysical plasmas.« less
  • We describe single and double photoionization of two-electron atoms by photoabsorption at high incident photon energies {omega} (but still {omega}<<mc{sup 2}) using a unified approach based on asymptotic Fourier transform (AFT) theory modified by Coulombic interactions. Within this approach the matrix elements for photoabsorption processes at high energies can be understood in terms of the singularities of the many-body Coulomb potential. These singularities (e-e and e-N) result in the singularities of the wave functions and the singularities of the e-{gamma} interaction, which determine the asymptotic behavior of the matrix element. Within our unified approach we explain the dominant contributions, includingmore » both the dominant contributions to the total cross section for single ionization and for ionization with excitation, and the dominant contributions to the double ionization spectrum, as a Fourier transform asymptotic in a single large momentum (dependent on the process and the region of the spectrum). These dominant contributions are connected, through AFT, with either the e-N singularity or the e-e singularity. The AFT results are modified by Coulombic interactions. We include these modifications, for the cases of single ionization and of double ionization in the shake-off region at high energies, and extract a slowly convergent factor (Stobbe factor). In this way we obtain rapid convergence of the cross sections to their high-energy behaviors. This also allows us to discuss the convergence of ratios of cross sections.« less
  • The R-matrix program is used to calculate collision strengths Omega for 190 fine-structure transitions among the 1s2 2s2 2p2, 1s2 2s 2p3, and 1s2 2p4 configurations of Ca XV in the energy range of 0-100 Ry. Relativistic effects are included in the computations of Omega through term coupling coefficients. The effective collision strengths Tau, obtained by averaging Omega over a Maxwellian distribution of electron velocities, are listed for all transitions in the temperature range of 10 to the 6th to 10 to the 7th K. The effects on the calculated Omega and Tau values of term coupling and configuration-interaction inmore » the target are examined, and the importance of including relativistic effects is noted, particularly for spin and parity changing transitions at the higher energies and temperatures. 35 refs.« less