Effect of the variation of electronic dipole moment on theoretical spectra: application to the λ Bootis stars

Allard, N. F.; Drira, I.; Faraggiana, R.; Gerbaldi, M.; Kielkopf, John F.; Kurucz, Robert L.

doi:10.1063/1.58367

Cited by 26 publications

(54 citation statements)

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“…The opacity package of the DETAIL code was updated by including the quasi-molecular Lyman α satellites following the implementation by Castelli & Kurucz (2001) of the Allard et al (1998) theory and using the Opacity Project (see Seaton et al 1994, for a general review) photoionization cross-sections for the calculations of b− f absorption of C i, N i, Mg i, Si i, Al i, and Fe i. In addition to the continuous background opacity, the line opacity introduced by H i and metal lines was taken into account by explicitly including it in solving the radiation transfer.…”

Section: Programs and Model Atmospheresmentioning

confidence: 99%

A non-LTE study of neutral and singly-ionized iron line spectra in 1D models of the Sun and selected late-type stars

Mashonkina

Gehren

Shi

et al. 2011

A&A

231

266

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Aims. We evaluate non-local thermodynamical equilibrium (non-LTE) line formation for the two ions of iron and check the ionization equilibrium between Fe i and Fe ii in model atmospheres of the cool reference stars based on the best available complete model atom for neutral and singly-ionized iron.Methods. We present a comprehensive model atom for Fe with more than 3000 measured and predicted energy levels. As a test and first application of the improved model atom, iron abundances are determined for the Sun and five stars with well determined stellar parameters and high-quality observed spectra. The efficiency of inelastic collisions with hydrogen atoms in the statistical equilibrium of iron is empirically estimated from inspection of their different influence on the Fe i and Fe ii lines in the selected stars. Results. Non-LTE leads to systematically depleted total absorption in the Fe i lines and to positive abundance corrections in agreement with the previous studies, however, the magnitude of such corrections is smaller compared to the earlier results. These non-LTE corrections do not exceed 0.1 dex for the solar metallicity and mildly metal-deficient stars, and they vary within 0.21 dex and 0.35 dex in the very metal-poor stars HD 84937 and HD 122563, respectively, depending on the assumed efficiency of collisions with hydrogen atoms. Based on the analysis of the Fe i/Fe ii ionization equilibrium in these two stars, we recommend to apply the Drawin formalism in non-LTE studies of Fe with a scaling factor of 0.1. For the Fe ii lines non-LTE corrections do not exceed 0.01 dex in absolute value over the whole range of stellar parameters that are considered. This study reveals two problems. The first one is that g f -values available for the Fe i and Fe ii lines are not accurate enough to pursue high-accuracy absolute stellar abundance determinations. For the Sun, the mean non-LTE abundance obtained from 54 Fe i lines is 7.56 ± 0.09 and the mean abundance from 18 Fe ii lines varies between 7.41 ± 0.11 and 7.56 ± 0.05 depending on the source of the g f -values. The second problem is that lines of Fe i give, on average, a 0.1 dex lower abundance compared with those of Fe ii lines for HD 61421 and HD 102870, even when applying a differential line-by-line analysis with regard to the Sun. A disparity between neutral atoms and first ions points to problems of stellar atmosphere modelling or/and effective temperature determination.

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Section: Programs and Model Atmospheresmentioning

confidence: 99%

A non-LTE study of neutral and singly-ionized iron line spectra in 1D models of the Sun and selected late-type stars

Mashonkina

Gehren

Shi

et al. 2011

A&A

231

266

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“…For C, N, and O, abundances log(N elem /Ntot) equal to −3.85, −3.99, and −3.11, respectively, were adopted. We selected λ Boo in order to compare results from the new-ODFs with those from Allard et al (1998aAllard et al ( , 1998b, who tested their semi-classical computations of the H-H and H-H + quasi-molecular absorptions on this star. The analysis of the IUE high-resolution spectrum has shown that lines of H2 are a very important source of line opacity for λ Boo shortward 1600Å.…”

mentioning

confidence: 99%

Ultraviolet spectra forλBoo (HD 125162) computed with H$_{\mathsf 2}$ opacities and Lyman-αH-H and H-H⁺opacities

Castelli

Kurucz²

2001

A&A

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Abstract. New opacity distribution functions (ODF) have been computed for use with the ATLAS9 model atmosphere code of Kurucz. One of the improvements upon the Kurucz (1990) ODFs is the addition to the line blanketing of the Lyman-α H-H and H-H + quasi-molecular absorptions near 1600Å and 1400Å. New-ODF fluxes are expected to reproduce the ultraviolet observations of λ Boo stars and metal-poor A-type stars in a more realistic way than previous computations did. In this paper we compare low-and high-resolution IUE observations of λ Boo (HD 125162, HR 5351) with fluxes and synthetic spectra based on ATLAS9 models and new-ODFs, which were computed for [M/H] = −2.0 for all the elements, except CNO. For C, N, and O, abundances log(N elem /Ntot) equal to −3.85, −3.99, and −3.11, respectively, were adopted. We selected λ Boo in order to compare results from the new-ODFs with those from Allard et al. (1998aAllard et al. ( , 1998b, who tested their semi-classical computations of the H-H and H-H + quasi-molecular absorptions on this star. The analysis of the IUE high-resolution spectrum has shown that lines of H2 are a very important source of line opacity for λ Boo shortward 1600Å. When both atomic and molecular lines are considered, the slope of the observed energy distribution is well reproduced in the whole region 1300-3000Å by the new-ODF model, but the H-H quasi-molecular absorption at 1600Å is computed about 10% too strong. The fit of the low-resolution IUE image SWP17872 to a small grid of new-ODF models gives parameters T eff = 8650 K, log g = 4.0, while the fit of the high-resolution image SWP42081, rebinned at the low resolution wavelength step size, gives parameters T eff = 8500 K, log g = 4.0. These last parameters are in close agreement with T eff = 8550 K, log g = 4.1 obtained by fitting the visible energy distribution. The different IUE images are discussed.

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“…Recent progress has been made by including the variation of the radiative dipole moment during the collision for the Lyman /? line (H-H+ satellites, Allard et al 1998a) and for the Lyman a line (H-H, and H-H+ satellites, Allard et al 1998b).…”

Section: Isolated Linesmentioning

confidence: 99%

Commission 14: Atomic and Molecular Data: (Donnees Atomiques et Moleculaires)

Rostas¹,

Smith²,

Berrington³

et al. 2000

Trans. Int. Astron. Union

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In recognition of its special interdisciplinary character, IAU Commission 14 is linked directly to the Executive Committee. The Commission’s role is to inform the astronomical community of new developments in the diverse fields of research which involve atoms and molecules. Conversely it endeavors to sensitize the research community active in those fields to the specific needs of astronomy, especially concerning basic data and modeling tools. More generally, Commission 14 tries to foster long term relations and collaborations between the two communities and, when necessary, to alert funding authorities to the specific needs of ground and space based astronomy for specific atomic and molecular data. This report is one of the main contributions of Commission 14 to the information of the astronomical community. Several meetings concerned, at least in part, with the need and availability of atomic and molecular data for astrophysics were also sponsored or co-sponsored. In the last triennium, Commission 14 cosponsored IAU Symposium 194 “Astrochemistry: From Molecular Cloud to Planetary Systems” held in Sogwipo (Korea) from Aug. 23 to 27, 1999 and organized by Commission 34. A Joint Discussion: JD1 on “Atomic and Molecular Data for Astrophysics, New Developments, Case Studies and Future Needs” has been planned for the XXIVth IAU General Assembly in Manchester (Aug. 7-19, 2000) and cosponsored by Commissions 15, 16, 29, 34, 36, 40 and 44. Several other Joint Discussions to be held at the Manchester General Assembly are co-sponsored by this commission.

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Effect of the variation of electronic dipole moment on theoretical spectra: application to the λ Bootis stars

Cited by 26 publications

References 0 publications

A non-LTE study of neutral and singly-ionized iron line spectra in 1D models of the Sun and selected late-type stars

A non-LTE study of neutral and singly-ionized iron line spectra in 1D models of the Sun and selected late-type stars

Ultraviolet spectra forλBoo (HD 125162) computed with H$_{\mathsf 2}$ opacities and Lyman-αH-H and H-H⁺opacities

Commission 14: Atomic and Molecular Data: (Donnees Atomiques et Moleculaires)

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Effect of the variation of electronic dipole moment on theoretical spectra: application to the λ Bootis stars

Cited by 26 publications

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A non-LTE study of neutral and singly-ionized iron line spectra in 1D models of the Sun and selected late-type stars

A non-LTE study of neutral and singly-ionized iron line spectra in 1D models of the Sun and selected late-type stars

Ultraviolet spectra forλBoo (HD 125162) computed with H$_{\mathsf 2}$ opacities and Lyman-αH-H and H-H+opacities

Commission 14: Atomic and Molecular Data: (Donnees Atomiques et Moleculaires)

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Ultraviolet spectra forλBoo (HD 125162) computed with H$_{\mathsf 2}$ opacities and Lyman-αH-H and H-H⁺opacities