K. M. Aggarwal

Queen's University Belfast, Béal Feirste, Northern Ireland, United Kingdom

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Publications (226)619.11 Total impact

  • Kanti M. Aggarwal
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    ABSTRACT: Recently, S. Aggarwal et al. [Chin. Phys. B 24 (2015) 053201] reported energy levels, radiative rates, and lifetimes for the lowest 148 levels belonging to the 3s23p, 3s3p2, 3s23d, 3s3p3d, 3p3, 3p23d, 3s3d2, 3p3d2, and 3d3 configurations of Al-like tungsten. While their calculated energies for the levels and the radiative rates for transitions are correct, the reported results for lifetimes are completely wrong. According to our calculations, errors in their reported lifetimes are up to 14 orders of magnitude for over 90% of the levels. Here we report the correct lifetimes and explain the reasons for discrepancies.
    No preview · Article · Dec 2015 · Chinese Physics B
  • Kanti M. Aggarwal · Francis P. Keenan
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    ABSTRACT: Calculations of energy levels, radiative rates and lifetimes are reported for 17 F-like ions with 37 $\le$ Z $\le$ 53. For brevity, results are only presented among the lowest 113 levels of the 2s$^2$2p$^5$, 2s2p$^6$, 2s$^2$2p$^4$3$\ell$, 2s2p$^5$3$\ell$, and 2p$^6$3$\ell$ configurations, although the calculations have been performed for up to 501 levels in each ion. The general-purpose relativistic atomic structure package (GRASP) has been adopted for the calculations, and radiative rates (along with oscillator strengths and line strengths) are listed for all E1, E2, M1, and M2 transitions of the ions. Comparisons are made with earlier available experimental and theoretical energies, although these are limited to only a few levels for most ions. Therefore for additional accuracy assessments, particularly for energy levels, analogous calculations have been performed with the Flexible Atomic Code (FAC), for up to 72~259 levels. Limited previous results are available for radiative rates for comparison purposes, and no large discrepancy is observed for any transition and/or ion.
    No preview · Article · Dec 2015 · Atomic Data and Nuclear Data Tables
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    ABSTRACT: Recent atomic physics calculations for Si ii are employed within the cloudy modelling code to analyse Hubble Space Telescope (HST) STIS ultraviolet spectra of three cool stars, β Geminorum, α Centauri A and B, as well as previously published HST/GHRS observations of α Tau, plus solar quiet Sun data from the High Resolution Telescope and Spectrograph. Discrepancies found previously between theory and observation for line intensity ratios involving the 3s23p 2PJ–3s3p2 4P$_{J^{\prime }}$ intercombination multiplet of Si ii at ∼ 2335 Å are significantly reduced, as are those for ratios containing the 3s23p 2PJ–3s3p2 2D$_{J^{\prime }}$ transitions at ∼1816 Å. This is primarily due to the effect of the new Si ii transition probabilities. However, these atomic data are not only very different from previous calculations, but also show large disagreements with measurements, specifically those of Calamai et al. for the intercombination lines. New measurements of transition probabilities for Si ii are hence urgently required to confirm (or otherwise) the accuracy of the recently calculated values. If the new calculations are confirmed, then a long-standing discrepancy between theory and observation will have finally been resolved. However, if the older measurements are found to be correct, then the agreement between theory and observation is simply a coincidence and the existing discrepancies remain.
    Full-text · Article · Oct 2015 · Monthly Notices of the Royal Astronomical Society
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    ABSTRACT: We report calculations of energy levels and radiative rates ($A$-values) for transitions in Cr-like Co IV and Ni V. The quasi-relativistic Hartree-Fock (QRHF) code is adopted for calculating the data although GRASP (general-purpose relativistic atomic structure package) and flexible atomic code (FAC) have also been employed for comparison purposes. No radiative rates are available in the literature to compare with our results, but our calculated energies are in close agreement with those compiled by NIST for a majority of the levels. However, there are discrepancies for a few levels of up to 3\%. The $A$-values are listed for all significantly contributing E1, E2 and M1 transitions, and the corresponding lifetimes reported, although unfortunately no previous theoretical or experimental results exist to compare with our data.
    Full-text · Article · Sep 2015 · Atomic Data and Nuclear Data Tables
  • Kanti M. Aggarwal

    No preview · Article · Aug 2015 · Journal of Quantitative Spectroscopy and Radiative Transfer
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    Kanti M. Aggarwal · Francis P. Keenan
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    ABSTRACT: Energies and lifetimes are reported for the eight Br-like ions with 43 $\le$ Z $\le$ 50, namely Tc ~IX, Ru~X, Rh~XI, Pd~XII, Ag~XIII, Cd~XIV, In~XV, and Sn~XVI. Results are listed for the lowest 375 levels, which mostly belong to the 4s$^2$4p$^5$, 4s$^2$4p$^4$4$\ell$, 4s4p$^6$, 4s$^2$4p$^4$5$\ell$, 4s$^2$4p$^3$4d$^2$, 4s4p$^5$4$\ell$, and 4s4p$^5$5$\ell$ configurations. Extensive configuration interaction among 39 configurations (generating 3990 levels) has been considered and the general-purpose relativistic atomic structure package ({\sc grasp}) has been adopted for the calculations. Radiative rates are listed for all E1, E2, M1, and M2 transitions involving the lowest 375 levels. Previous experimental and theoretical energies are available for only a few levels of three, namely Ru~X, Rh~XI and Pd~XII. Differences with the measured energies are up to 4\% but the present results are an improvement (by up to 0.3 Ryd) in comparison to other recently reported theoretical data. Similarly for radiative rates and lifetimes, prior results are limited to those involving only 31 levels of the 4s$^2$4p$^5$, 4s$^2$4p$^4$4d, and 4s4p$^6$configurations for the last four ions. Moreover, there are generally no discrepancies with our results, although the larger calculations reported here differ by up to two orders of magnitude for a few transitions.
    Preview · Article · Jul 2015 · Atomic Data and Nuclear Data Tables
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    Kanti M. Aggarwal · Francis P. Keenan
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    ABSTRACT: Energies and lifetimes are reported for the lowest 375 levels of five Br-like ions, namely Sr~IV, Y~V, Zr~VI, Nb~VII, and Mo~VIII, mostly belonging to the 4s$^2$4p$^5$, 4s$^2$4p$^4$4$\ell$, 4s4p$^6$, 4s$^2$4p$^4$5$\ell$, 4s$^2$4p$^3$4d$^2$, 4s4p$^5$4$\ell$, and 4s4p$^5$5$\ell$ configurations. Extensive configuration interaction has been included and the general-purpose relativistic atomic structure package ({\sc grasp}) has been adopted for the calculations. Additionally, radiative rates are listed among these levels for all E1, E2, M1, and M2 transitions. From a comparison with the measurements, the majority of our energy levels are assessed to be accurate to better than 2\%, although discrepancies between theory and experiment for a few are up to 6\%. An accuracy assessment of the calculated radiative rates (and lifetimes) is more difficult, because no prior results exist for these ions.
    Preview · Article · Apr 2015 · Atomic Data and Nuclear Data Tables
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    K M Aggarwal · F P Keenan
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    ABSTRACT: Energy levels, radiative rates, lifetimes, collision strengths and effective collision strengths are calculated for two important Al-like ions, namely Si II and Fe XIV. For Si II, the lowest 56 levels of the 3s23p, 3s3p2 3p3 3s23d, 3s3p3d, 3s24ℓ and 3s25ℓ configurations are included, whereas for Fe XIV additional 80 levels of 3p23d, 3s3d2 and 3p3d2 are considered, but not of 3s2 5ℓ. For the determination of atomic structure GRASP has been adopted and radiative rates are calculated for all E1, E2, Ml and M2 transitions. Electron impact excitation collision strengths are calculated with the DARC code, over a wide energy range, and resonances are resolved in a fine energy mesh to determine effective collision strengths over a wide range of temperatures. Extensive comparisons are made for all atomic parameters with available theoretical and experimental data, and the accuracy of the present results is assessed. Energy levels are estimated to be accurate to ~1% and all other parameters to be better than 20%.
    Preview · Article · Jan 2015 · Journal of Physics Conference Series
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    Kanti M. Aggarwal · Francis P. Keenan
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    ABSTRACT: 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 (ϒ) 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 ϒ, 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 ϒ, highlight the large discrepancies for a significant number of transitions and suggest possible reasons for these.
    Preview · Article · Jan 2015 · Monthly Notices of the Royal Astronomical Society
  • Kanti M. Aggarwal · Francis P. Keenan
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    ABSTRACT: We report calculations of energy levels, radiative decay rates, and lifetimes for transitions among the 3s(2)3p(5), 3s3p(6), and 3s(2)3p(4)3d configurations of Cl-like W LVIII. The general-purpose relativistic atomic structure package (GRASP) has been adopted for our calculations. Comparisons are made with the most recent results of Mohan et al. (Can. J. Phys. 92, 177 (2014). doi: 10.1139/cjp-2013-0348) and discrepancies in lifetimes are noted, up to four orders of magnitude in some instances. Our energy levels are estimated to be accurate to better than 0.5%, whereas results for radiative rates and lifetimes should be accurate to better than 20%.
    No preview · Article · Oct 2014 · Canadian Journal of Physics
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    Kanti M. Aggarwal · Francis P. Keenan
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    ABSTRACT: Energy levels and radiative rates for transitions in five Br-like ions (Sr IV, Y V, Zr VI, Nb VII and Mo VIII) are calculated with the general-purpose relativistic atomic structure package ({\sc grasp}). Extensive configuration interaction has been included and results are presented among the lowest 31 levels of the 4s$^2$4p$^5$, 4s$^2$4p$^4$4d and 4s4p$^6$ configurations. Lifetimes for these levels have also been determined, although unfortunately no measurements are available with which to compare. However, recently theoretical results have been reported by Singh {\em et al} [Phys. Scr. {\bf 88} (2013) 035301] using the same {\sc grasp} code. But their reported data for radiative rates and lifetimes cannot be reproduced and show discrepancies of up to five orders of magnitude with the present calculations.
    Preview · Article · Sep 2014 · Physica Scripta
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    Kanti M Aggarwal · Francis P Keenan
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    ABSTRACT: 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 ({\sc grasp}) is adopted, while 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 listed for all E1, E2, M1 and M2 transitions among the lowest 98 levels of the $n \le$ 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 10$^{7.8}$ K, depending on the ion.
    Preview · Article · Sep 2014 · Physica Scripta
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    Kanti M. Aggarwal · Francis P. Keenan
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    ABSTRACT: Energy levels and radiative rates are reported for transitions in Cl-like W LVIII. Configuration interaction (CI) has been included among 44 configurations (generating 4978 levels) over a wide energy range up to 363 Ryd, and the general-purpose relativistic atomic structure package ({\sc grasp}) adopted for the calculations. Since no other results of comparable complexity are available, calculations have also been performed with the flexible atomic code ({\sc fac}), which help in assessing the accuracy of our results. Energies are listed for the lowest 400 levels (with energies up to $\sim$ 98 Ryd), which mainly belong to the 3s$^2$3p$^5$, 3s3p$^6$, 3s$^2$3p$^4$3d, 3s$^2$3p$^3$3d$^2$, 3s3p$^4$3d$^2$, 3s$^2$3p$^2$3d$^3$, and 3p$^6$3d configurations, and radiative rates are provided for four types of transitions, i.e. E1, E2, M1, and M2. Our energy levels are assessed to be accurate to better than 0.5%, whereas radiative rates (and lifetimes) should be accurate to better than 20% for a majority of the strong transitions.
    Preview · Article · Jun 2014 · Atomic Data and Nuclear Data Tables
  • KM Aggarwal · FP Keenan
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    ABSTRACT: Energies for the lowest 56 levels, belonging to the 3s$^2$3p, 3s3p$^2$, 3p$^3$, 3s$^2$3d, 3s3p3d, 3s$^2$4$\ell$ and 3s$^2$5$\ell$ configurations of Si II, are calculated using the {\sc grasp} (General-purpose Relativistic Atomic Structure Package) code. Analogous calculations have also been performed (for up to 175 levels) using the Flexible Atomic Code ({\sc fac}). Furthermore, radiative rates are calculated for all E1, E2, M1 and M2 transitions. Extensive comparisons are made with available theoretical and experimental energy levels, and the accuracy of the present results is assessed to be better than 0.1 Ryd. Similarly, the accuracy for radiative rates (and subsequently lifetimes) is estimated to be better than 20% for most of the (strong) transitions. Electron impact excitation collision strengths are also calculated, with the Dirac Atomic R-matrix Code ({\sc darc}), over a wide energy range up to 13 Ryd. Finally, to determine effective collision strengths, resonances are resolved in a fine energy mesh in the thresholds region. These collision strengths are averaged over a Maxwellian velocity distribution and results listed over a wide range of temperatures, up to 10$^{5.5}$ K. Our data are compared with earlier $R$-matrix calculations and differences noted, up to a factor of two, for several transitions. Although scope remains for improvement, the accuracy for our results of collision strengths and effective collision strengths is assessed to be about 20% for a majority of transitions.
    No preview · Article · Apr 2014
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    K. M. Aggarwal · F. P. Keenan
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    ABSTRACT: We report calculations of energy levels, radiative decay rates, and lifetimes for transitions among the 3s$^2$3p$^5$, 3s3p$^6$, and 3s$^2$3p$^4$3d configurations of Cl-like W LVIII. The general-purpose relativistic atomic structure package (GRASP) has been adopted for our calculations. Comparisons are made with the most recent results of Mohan et al. [Can. J. Phys. {\bf 92} (2014) xxx] and discrepancies in lifetimes are noted, up to four orders of magnitude in some instances. Our energy levels are estimated to be accurate to better than 0.5\%, whereas results for radiative rates and lifetimes should be accurate to better than 20\%.
    Preview · Article · Jan 2014
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    K. M. Aggarwal · F. P. Keenan
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    ABSTRACT: Energies and lifetimes are reported for the lowest 136 levels of Fe xiv, belonging to the (1s22s22p6) 3s23p, 3s3p2, 3s23d, 3p3, 3s3p3d, 3p23d, 3s3d2, 3p3d2 and 3s24ℓ 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 107.1 K. Comparisons are made with available results in the literature, and the accuracy of the present data is assessed.
    Preview · Article · Nov 2013 · Monthly Notices of the Royal Astronomical Society
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    KM Aggarwal · FP Keenan
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    ABSTRACT: We report calculations of energy levels, radiative rates, oscillator strengths and line strengths for transitions among the lowest 231 levels of Ti VII. The general-purpose relativistic atomic structure package ({\sc grasp}) and flexible atomic code ({\sc fac}) are adopted for the calculations. Radiative rates, oscillator strengths and line strengths are provided for all electric dipole (E1), magnetic dipole (M1), electric quadrupole (E2) and magnetic quadrupole (M2) transitions among the 231 levels, although calculations have been performed for a much larger number of levels (159,162). In addition, lifetimes for all 231 levels are listed. Comparisons are made with existing results and the accuracy of the data is assessed. In particular, the most recent calculations reported by Singh {\em et al} [Can J. Phys. {\bf 90} (2012) 833] are found to be unreliable, with discrepancies for energy levels of up to 1 Ryd and for radiative rates of up to five orders of magnitude for several transitions, particularly the weaker ones. Based on several comparisons among a variety of calculations with two independent codes, as well as with the earlier results, our listed energy levels are estimated to be accurate to better than $1\%$ (within 0.1 Ryd), whereas results for radiative rates and other related parameters should be accurate to better than $20\%$.
    Preview · Article · Nov 2013 · Physica Scripta
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    Kanti M. Aggarwal · Francis P. Keenan
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    ABSTRACT: We report calculations of energy levels and oscillator strengths for transitions in W XL, undertaken with the general-purpose relativistic atomic structure package ({\sc grasp}) and flexible atomic code ({\sc fac}). Comparisons are made with existing results and the accuracy of the data is assessed. Discrepancies with the most recent results of S. Aggarwal et al. [Can. J. Phys. {\bf 91} (2013) 394] are up to 0.4 Ryd and up to two orders of magnitude for energy levels and oscillator strengths, respectively. Discrepancies for lifetimes are even larger, up to four orders of magnitude for some levels. Our energy levels are estimated to be accurate to better than 0.5% (i.e. 0.2 Ryd), whereas results for oscillator strengths and lifetimes should be accurate to better than 20%.
    Preview · Article · Oct 2013 · Canadian Journal of Physics
  • KM Aggarwal · FP Keenan
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    ABSTRACT: We report calculations of energy levels, radiative rates, oscillator strengths and line strengths for transitions among the lowest 345 levels of Ti X. These include 146 levels of the $n \le$ 3 configurations and 86 of 3s$^2 4\ell$, 3s$^2 5\ell$ and 3s3p4$\ell$, plus some of the 3s$^2 6\ell$, 3p$^2 4\ell$ and 3s3p5$\ell$ levels. The general-purpose relativistic atomic structure package ({\sc grasp}) and flexible atomic code ({\sc fac}) are adopted for the calculations. Radiative rates, oscillator strengths and line strengths are provided for all electric dipole (E1), magnetic dipole (M1), electric quadrupole (E2) and magnetic quadrupole (M2) transitions among the 345 levels, although calculations have been performed for a much larger number of levels. Comparisons are made with existing results and the accuracy of the data is assessed. Additionally, lifetimes for all 345 levels are listed. Extensive comparisons of lifetimes are made for the lowest 40 levels, for which discrepancies with recent theoretical work are up to 30%. Discrepancies in lifetimes are even larger, up to a factor of four, for higher excited levels. Furthermore, the effect of large CI is found to be insignificant for both the energies and lifetimes for the lowest 40 levels of Ti X which belong to the 3s$^2$3p, 3s3p$^2$, 3s$^2$3d, 3p$^3$ and 3s3p3d configurations. However, the contribution of CI is more appreciable for the energy levels and radiative rates among higher excited levels. Our listed energy levels are estimated to be accurate to better than 1% (within 0.1 Ryd), whereas results for other parameters are probably accurate to better than 20%.
    No preview · Article · Jul 2013
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    K.M. Aggarwal · F.P. Keenan · A.Z. Msezane
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    ABSTRACT: Energy levels and radiative rates for fine-structure transitions in nickel ions (Ni XIII–XVI) have been calculated using the GRASP code. Configuration interaction and relativistic effects have been included, and comparisons are made with available data. Energy levels and radiative rates are tabulated for transitions among the 48, 43, 32, and 84 levels of Ni XIII, Ni XIV, Ni XV, and Ni XVI, respectively. The energy levels are assessed to be accurate to better than 5% for a majority of levels, while oscillator strengths for all strong transitions are accurate to better than 20%.
    Preview · Article · Jul 2013 · Atomic Data and Nuclear Data Tables

Publication Stats

2k Citations
619.11 Total Impact Points

Institutions

  • 1982-2015
    • Queen's University Belfast
      • • Astrophysics Research Centre (ARC)
      • • Department of Physics and Astronomy
      • • Department of Applied Mathematics & Theoretical Physics
      Béal Feirste, Northern Ireland, United Kingdom
  • 1988-2006
    • University of Delhi
      • Department of Physics & Astrophysics
      Delhi, NCT, India
  • 1998
    • University of Malaya
      Kuala Lumpor, Kuala Lumpur, Malaysia