The oscillator strength of the SI II 3s2 3p (P-2)-3s3p2 D-2 multiplet and the interstellar abundance of silicon

Dufton, P. L.; Keenan, F. P.; Hibbert, A; Ojha, Piyush; Stafford, R. P.

doi:10.1086/171093

Cited by 28 publications

(24 citation statements)

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“…As can be seen in Table A measured LS multiplet value with the present f-value is fair, while the agreement is good with the present J = 1/2-3/2 fine-structure component. Their results also agree well with the atomic structure calculations of Hibbert et al [13] for the LS multiplet and reasonably well with those of Dufton et al [12] for the fine-structure transitions. The present gf value agrees quite well with that given by Mendoza et al [10] for this transition and for other transitions.…”

Section: Resultssupporting

confidence: 88%

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OSCILLATOR STRENGTHS FOR DIPOLE-ALLOWED FINE-STRUCTURE TRANSITIONS IN Si II

Nahar

1998

Atomic Data and Nuclear Data Tables

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An extensive dataset of oscillator strengths, line strengths, and Einstein A -coefficients has been calculated for a large number of dipole-allowed (ΔS=0) fine-structure transitions in Si II. The line strengths in LS coupling are obtained in an ab initio manner in the close-coupling approximation employing the R-matrix method. The fine-structure components are obtained through algebraic transformations of the LS multiplets. Observed spectroscopic energies are employed whenever available. A 12-state eigenfunction expansion of the core ion, Si III, is employed for the present calculations. This work presents the oscillator strengths of 1122 fine-structure transitions in Si II corresponding to 390 LS multiplets and provides a reasonably complete set of radiative transitions for this astrophysically important ion for the first time. Present results are of comparable accuracy to previous detailed calculations obtained for a small number of transitions and are in reasonably good agreement with the measured oscillator strengths and lifetimes. INTRODUCTIONSi II is one of the most common ions observed in absorption and emission spectra from astrophysical sources, such as the interstellar medium, quasars, hot stars, and the sun. The oscillator strengths for transitions in Si II are used in the determination of abundances, temperatures, densities, and column densities (see, e.g., Ref.[1]). Si II has been investigated both experimentally [2][3][4][5][6][7][8][9] and theoretically [10][11][12][13][14][15][16][17] by many workers. However, all these studies have remained confined to a limited number of transitions until the work of the Opacity Project (OP) [10]. One of the aims of the OP [18] has been to obtain accurate atomic radiative data in an ab initio manner in the close-coupling (CC) approximation using the R-matrix method. The radiative work of the OP was carried out in LS coupling; however, the laboratory plasma experiments and the various astrophysical models usually consider the fine-structure transitions (see, e.g., [2][3][4][5]). The extended non-LTE (low temperature equilibrium) models which consider a number of transitions, such as ones observed in hot stars, require both radiative and collisional data for a large number of energy levels. Collisional data are now available for Si II [19] obtained in the close-coupling approximation using the R-matrix method. The aim of this work is to present an extensive set of radiative data of reliable accuracy for fine-structure transitions in Si II to be used in collisional-radiative models employed in astrophysical applications. Similar sets of data for fine-structure transitions in other ions employing the present method have been reported earlier [20]. Summary of the Theoretical Work and ComputationsThe calculations of the oscillator strengths (f-values), line strengths (S-values), and Einstein coefficients or transition probabilities (A-values) have been described in previous works [20] and are not discussed in detail here. We present only the computational details pe...

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Section: Resultssupporting

confidence: 88%

“…[1]). Si II has been investigated both experimentally [2][3][4][5][6][7][8][9] and theoretically [10][11][12][13][14][15][16][17] by many workers. However, all these studies have remained confined to a limited number of transitions until the work of the Opacity Project (OP) [10].…”

Section: Introductionmentioning

confidence: 99%

OSCILLATOR STRENGTHS FOR DIPOLE-ALLOWED FINE-STRUCTURE TRANSITIONS IN Si II

Nahar

1998

Atomic Data and Nuclear Data Tables

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“…We deblended the Si iv λ 1393 line from the broad, deep stellar line at ∼150 km s −1 by fitting the stellar feature with a Gaussian profile. For Si ii λλ 1304 and 1526, we have adopted the f ‐values from Dufton et al (1983, 1992), as other studies (e.g. Spitzer & Fitzpatrick 1993) indicate that they are more accurate than other estimates.…”

Section: Discussionmentioning

confidence: 99%

HST/STIS observations of the high-velocity interstellar cloud HVC 291.2-41.2+80: a warm, mainly ionized high-velocity cloud

Lehner¹,

Keenan²,

Sembach³

2001

Monthly Notices of the Royal Astronomical Society

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We present intermediate‐resolution HST/STIS spectra of a high‐velocity interstellar cloud (vLSR=+80 km s−1) towards DI 1388, a young star in the Magellanic Bridge located between the Small and Large Magellanic Clouds. The STIS data have a signal‐to‐noise ratio (S/N) of 20–45 and a spectral resolution of about 6.5 km s−1 (FWHM). The high‐velocity cloud absorption is observed in the lines of C ii, O i, Si ii, Si iii, Si iv and S iii. Limits can be placed on the amount of S ii and Fe ii absorption that is present. An analysis of the relative abundances derived from the observed species, particularly C ii and O i, suggests that this high‐velocity gas is warm (Tk∼103–104 K) and predominantly ionized. This hypothesis is supported by the presence of absorption produced by highly ionized species, such as Si iv. This sightline also intercepts two other high‐velocity clouds that produce weak absorption features at vLSR=+113 and +130 km s−1 in the STIS spectra.

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“…Our results for the weak transitions within the 3s 2 3p 2 P o J Y3s3p 2 2 D J 0 multiplet agreed with experiment to within 16%, and for intercombination 3s 2 3p 2 P o J Y3s3p 2 4 P J 0 transitions to about 25%. The other fairly extensive theoretical studies of oscillator strengths include configuration-interaction (CI ) calculations of Dufton & Kingston (1991), Dufton et al (1992), and Froese Fischer et al (2006) and LS R-matrix plus algebraic transformation calculation of Nahar (1998). The calculation of Tayal (2007) showed a very good agreement with the calculations of Froese Fischer et al (2006) and Nahar (1998) for transitions with significant oscillator strengths.…”

Section: Introductionmentioning

confidence: 99%

Collision Strengths for Electron Scattering from Siii

Tayal

2008

Astrophysical Journal Supplement Series, The

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Electron impact excitation collision strengths and rates for transitions between fine-structure levels of the 3s 2 np (n ¼ 3 Y6), 3s3p 2 , 3s 2 ns (n ¼ 4Y 6), 3s 2 nd (n ¼ 3 Y5), 3s 2 nf (n ¼ 4 Y5), and 3s3p3d configurations in Si ii are calculated by using the Breit-Pauli B-spline R-matrix approach. The 31 target levels have been included in the closecoupling expansion in our collision calculation. The multiconfiguration Hartree-Fock method with term-dependent nonorthogonal orbitals is employed for an accurate representation of the target wave functions. The target levels have been described by using both spectroscopic and correlation radial functions. The atomic wave functions yield excitation energies that are in excellent agreement with experiment and other reliable calculations. The relativistic corrections are included through the one-body mass correction, Darwin, and spin-orbit operators in the Breit-Pauli Hamiltonian. The effective collision strengths have been calculated by integrating total resonant and nonresonant collision strengths over a Maxwellian distribution of electron energies, and these are presented over a wide temperature range suitable for modeling of astrophysical plasmas. Significant differences are noted with the previous eight-state R-matrix calculation, particularly for transitions involving higher excitation levels.

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The oscillator strength of the SI II 3s2 3p (P-2)-3s3p2 D-2 multiplet and the interstellar abundance of silicon

Cited by 28 publications

References 0 publications

OSCILLATOR STRENGTHS FOR DIPOLE-ALLOWED FINE-STRUCTURE TRANSITIONS IN Si II

OSCILLATOR STRENGTHS FOR DIPOLE-ALLOWED FINE-STRUCTURE TRANSITIONS IN Si II

HST/STIS observations of the high-velocity interstellar cloud HVC 291.2-41.2+80: a warm, mainly ionized high-velocity cloud

Collision Strengths for Electron Scattering from Siii

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