Transition probabilities for dipole allowed fine structure transitions in Si-like ions: Si I, S III, Ar V and Ca VII

Astron. Astrophys. Suppl. Ser.

Pradhan

1999

Abstract. The first large-scale calculations of relativistic radiative transition probabilities from the Iron Project is reported for dipole allowed and intercombination (E1) transitions in Li-like Fe XXIV and He-like Fe XXV. The ab intio calculations are carried out in the close coupling approximation using the Breit-Pauli R-matrix method in intermediate coupling characterized by SLJ, with total (2S + 1) = 2,4, L = 7, J = 1/2 − 11/2 even and odd parity, for Fe XXIV, and with total (2S + 1) = 1,3, L = 9, and J = 0 − 4 for Fe XXV. The eigenfunction expansions for the target ions include 13 levels up to the n = 3 for Fe XXV, and 16 levels up to the n = 4 for Fe XXVI, respectively. The calculated number of bound levels, 83 for Fe XXIV and 138 for Fe XXV, is much larger than experimentally observed. The level energies are in good agreement for the common levels. All dipole and intercombination fine structure transitions involving the calculated bound levels up to n = 10 and = 5 or 6 are considered. Oscillator strengths, line strengths, and Einstein A-coefficients are tabulated for 802 transitions in Fe XXIV and 2579 transitions in Fe XXV. The results compare well with limited subsets of transitions considered in previous works including fully relativistic and QED corrections. Additional comparisons between the length and the velocity formulations indicate an overall accuracy between 1 − 10%. The range of uncertainty is indicative of the relatively small influence of atomic effects, such as the two-body Breit interaction terms and finite nuclear mass term, that are not included in the Breit-Pauli approximation employed in the present calculations. The extensive set of data is expected to be useful in the analysis of X-ray and XUV spectra from astrophysical sources 1 .Send offprint requests to: S.N. Nahar 1 The complete table of transition probabilities is available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.ustrasbg.fr/Abstract.html

Section: Introductionmentioning

confidence: 98%

Atomic data from the Iron Project

Astron. Astrophys. Suppl. Ser.

Pradhan

1999

“…Following an algebraic transformation of the LS multiplet line strengths to yield fine structure components, the atomic parameters for the dipole allowed transitions, oscillator strengths (f-values), line strengths (S), and the Einstein's A-coefficients (A-values), are obtained for a large number of fine structure transitions in Fe III. The method, applied to several other ions including Fe II (Nahar 1993(Nahar , 1995Nahar 1996 N2), is outlined in the next section.…”

Section: Introductionmentioning

confidence: 99%

Atomic data from the Iron Project. XVII. Radiative transition probabilities for dipole allowed and forbidden transitions in Fe III

Astron. Astrophys. Suppl. Ser.

Pradhan

1996

Abstract. -Transition probabilities are obtained for both the dipole allowed (E1) fine structure transitions and the forbidden electric quadrupole and magnetic dipole (E2, M1) transitions in Fe III. For the E1 transitions, ab initio calculations in the close coupling (CC) approximation using the R-matrix method are carried out in LS coupling with a 49-term eigenfunction expansion for Fe IV. The fine structure components are obtained through algebraic transformation of the LS line strengths, and the oscillator strengths and A-coefficients are computed using spectroscopic energies of the observed levels. Radiative transition probabilities for 9797 fine structure E1 transitions corresponding to 1408 LS multiplets among 200 bound states of Fe III are reported. Forbidden E2 and M1 transition probabilities are computed for 362 transitions among the 34 fine structure levels of all 16 LS terms dominated by the 3d 6 configuration using optimised configuration-interaction wavefunctions from the SUPERSTRUCTURE program in the Breit-Pauli approximation. Comparison of the present results is made with previous calculations and significant differences are found. Theoretical line ratios computed using the present E2 and M1 A-coefficients show better agreement with observations for some prominent Fe III lines in the infra-red than those using the earlier data by Garstang (1957). This work is carried out as part of the Iron Project to obtain accurate radiative and collisional data for the Iron group elements.

“…The aim of the present work is to provide a reasonably complete set of transition probabilities for fine-structure transitions through large scale ab initio calculations using the CC R-matrix method. Similar results for atomic transition probabilities have been obtained for other silicon-like ions, Si I, S III, Ar V, and Ca VII [15], and for iron ions, Fe II [16], Fe III [17], and Fe XXIV and Fe XXV [18]. A complementary set of data for the collision strengths for Fe XIII is being computed under the IP [12].…”

Section: Introductionmentioning

confidence: 63%

OSCILLATOR STRENGTHS FOR DIPOLE-ALLOWED FINE-STRUCTURE TRANSITIONS IN Fe XIII

Atomic Data and Nuclear Data Tables

1999

Oscillator strengths, line strengths, and transition probabilities for fine-structure levels in silicon-like iron, Fe XIII, are reported. The data obtained are for 1223 LS bound terms, 64,456 LS multiplets, and 307,863 fine-structure transitions. Calculations are carried out in LS coupling using the close coupling R-matrix approximation with a 14-term eigenfunction expansion. The fine-structure components are obtained through algebraic transformations. Present data considerably exceed the observed and the previously calculated data available, including those from the Opacity Project. Comparisons with previously measured and calculated values are made.