Browsing by Author "Palmeri, P."

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    Nitrogen K-Shell Photoabsorption
    Garcia, J.; Kallman, T. R.; Witthoeft, M.; Behar, E.; Mendoza, C.; Palmeri, P.; Quinet, P.; Bautista, M. A.; Klapisch, M. (IOP PUBLISHING LTD, 2009-12)
    Reliable atomic data have been computed for the spectral modeling of the nitrogen K lines, which may lead to useful astrophysical diagnostics. Data sets comprise valence and K-vacancy level energies, wavelengths, Einstein A-coefficients, radiative and Auger widths, and K-edge photoionization cross sections. An important issue is the lack of measurements that are usually employed to fine-tune calculations so as to attain spectroscopic accuracy. In order to estimate data quality, several atomic structure codes are used and extensive comparisons with previous theoretical data have been carried out. In the calculation of K photoabsorption with the Breit-Pauli R-matrix method, both radiation and Auger dampings, which cause the smearing of the K edge, are taken into account. This work is part of a wider project to compute atomic data in the X-ray regime to be included in the database of the popular XSTAR modeling code.
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    Radiative and Auger Decay Data for Modeling Nickel K Lines
    Palmeri, P.; Quinet, P.; Mendoza, C.; Bautista, M. A.; Garcia, J.; Witthoeft, M. C.; Kallman, T. R. (IOP PUBLISHING LTD, 2008-12)
    Radiative and Auger decay data have been calculated for modeling the K lines in ions of the nickel isonuclear sequence, from Ni(+) up to Ni(27+). Level energies, transition wavelengths, radiative transition probabilities, and radiative and Auger widths have been determined using Cowan's Hartree-Fock with relativistic corrections (HFR) method. Auger widths for the third-row ions (Ni(+)-Ni(10+)) have been computed using single-configuration average (SCA) compact formulae. Results are compared with data sets computed with the AUTOSTRUCTURE and MCDF atomic structure codes and with available experimental and theoretical values, mainly in highly ionized ions and in the solid state.
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    Radiative transition rates and collision strengths for Si II
    Bautista, M. A.; Quinet, P.; Palmeri, P.; Badnell, N. R.; Dunn, J.; Arav, Nahum (EDP SCIENCES, 2009-12)
    Aims. This work reports on radiative transition rates and electron impact excitation collision strengths for levels of the 3s(2)3p, 3s3p(2), 3s(2)4s, and 3s(2)3d configurations of Si II. Methods. The radiative data were computed using the Thomas-Fermi-Dirac-Amaldi central potential, but with the modifications introduced by Bautista (2008) that account for the effects of electron-electron interactions. We also introduce new schemes for the optimization of the variational parameters of the potential. Additional calculations were carried out with the Relativistic Hartree-Fock and the multiconfiguration Dirac-Fock methods. Collision strengths in LS-coupling were calculated in the close coupling approximation with the R-matrix method. Then, fine structure collision strengths were obtained by means of the intermediate-coupling frame transformation (ICFT) method which accounts for spin-orbit coupling effects. Results. We present extensive comparisons between the results of different approximations and with the most recent calculations and experiments available in the literature. From these comparisons we derive a recommended set of g f-values and radiative transition rates with their corresponding estimated uncertainties. We also study the effects of different approximations in the representation of the target ion on the electron-impact collision strengths. Our most accurate set of collision strengths were integrated over a Maxwellian distribution of electron energies and the resulting effective collision strengths are given for a wide range of temperatures. Our results present significant differences from recent calculations with the B-spline non-orthogonal R-matrix method. We discuss the sources of the differences.
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    Spectrum Synthesis Modeling of the X-Ray Spectrum of GRO J1655-40 Taken During the 2005 Outburst
    Kallman, T. R.; Bautista, M. A.; Goriely, S.; Mendoza, C.; Miller, J. M.; Palmeri, P.; Quinet, P.; Raymond, J. (IOP PUBLISHING LTD, 2009-08)
    The spectrum from the black hole X-ray transient GRO J1655-40 obtained using the Chandra High Energy Transmission Grating in 2005 is notable as a laboratory for the study of warm absorbers, and for the presence of many lines from odd-Z elements between Na and Co ( and Ti and Cr) not previously observed in X-rays. We present synthetic spectral models which can be used to constrain these element abundances and other parameters describing the outflow from the warm absorber in this object. We present results of fitting to the spectrum using various tools and techniques, including automated line fitting, phenomenological models, and photoionization modeling. We show that the behavior of the curves of growth of lines from H-like and Li-like ions indicate that the lines are either saturated or affected by filling-in from scattered or a partially covered continuum source. We confirm the conclusion of previous work by Miller et al., which shows that the ionization conditions are not consistent with wind driving due to thermal expansion. The spectrum provides the opportunity to measure abundances for several elements not typically observable in the X-ray band. These show a pattern of enhancement for iron peak elements, and solar or subsolar values for elements lighter than calcium. Models show that this is consistent with enrichment by a core-collapse supernova. We discuss the implications of these values for the evolutionary history of this system.