NLTE Spectral Line Formation in Three Dimensions

Nordlund, Åke

doi:10.1007/978-94-011-3554-2_7

Cited by 4 publications

(3 citation statements)

References 4 publications

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“…Such horizontal transfer e †ects are the result of the smoothing e †ect associated to the existing source function Ñuctuations (Spiegel 1960 ;Kneer & Trujillo Bueno 1987) and to the channeling e †ect associated to the existing opacity Ñuctuations (Cannon 1970 ;Trujillo Bueno & Kneer 1990). In a full three-dimensional radiative transfer investigation it will certainly be of interest to take into account the inÑuence of the Doppler shifts of the line radiation Ðelds (due to the velocity Ðeld of the threedimensional model) on the atomic level populations (Cannon 1985 ;Nordlund 1991 ;see also Shine 1975). The interested reader may obtain some additional information about horizontal radiative transfer e †ects from the threedimensional multilevel transfer calculations of Fabiani Bendicho & Trujillo Bueno (1999).…”

Section: Discussionmentioning

confidence: 99%

“…) in the atmospheres of cool stars can presently be achieved by applying the code MUGA-3D, a multilevel radiative transfer three-dimensional code (see Fabiani Bendicho & Trujillo Bueno 1999) based on the Gauss-Seidel iterative scheme that Trujillo Bueno & Fabiani Bendicho (1995) developed for RT applications. In order to undertake such a three-dimensional RT investigation for iron using as input the aforementioned threedimensional hydrodynamic stellar photospheric model, it is Ðrst important to investigate carefully the NLTE iron line formation issue neglecting the e †ects of horizontal RT (see for a review on this topic ; see also Nordlund 1991). This is the goal of the present paper as a preliminary step that we make prior to describing the aforementioned full three-dimensional multilevel transfer simulations.…”

Section: Introductionmentioning

confidence: 99%

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The Iron Line Formation Problem in Three‐dimensional Hydrodynamic Models of Solar‐like Photospheres

Shchukina

Bueno

2001

ApJ

157

197

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This paper presents the results of a detailed theoretical investigation of the iron line formation NLTE problem in a three-dimensional model of the solar photosphere, which we have obtained from a very recent radiation hydrodynamics simulation of solar surface convection. In this Ðrst paper we have neglected the e †ects of horizontal radiative transfer on the atomic level populations, but we have considered a realistic atomic model for iron that contains hundreds of radiative transitions from the UV to the IR. The self-consistent solutions of the kinetic and transfer equations have been obtained with a new NLTE code, which is based on very efficient iterative methods. We Ðnd that overionization due to the near-UV radiation Ðeld does take place but mainly in the granular atmospheric regions. This wellknown NLTE mechanism tends to produce underpopulation of all the Fe I levels and a very small overexcitation of the Fe II levels. All over the three-dimensional photospheric model Fe II is the dominant ionization stage. We Ðnd signiÐcant LTE versus NLTE discrepancies mainly for the low-excitation Fe I lines. This applies to both the vertically emergent proÐles from the granular regions and also to the spatially averaged proÐles. These discrepancies are due to the line opacity deÐcits that result from the aforementioned underpopulation of the Fe I levels. The emergent proÐles of the low-excitation lines of Fe I are thus weaker in NLTE than in LTE. In particular, the largest errors in the equivalent widths (due to the LTE assumption) are found for the weakest low-excitation lines of Fe I. We also give quantitative estimates of the errors in the temperature structure of semiempirical solar granulation models obtained via the application of LTE inversion techniques to several groups of Fe I lines. For instance, the widely used Fe I 6301 and 6302 lines tend to lead to an overestimation of about 100È200 K in the Ó granular regions but to a similar underestimation in the intergranular plasma.The present paper considers also the case of the Sun observed with low spatial resolution, with particular emphasis on the long-standing iron abundance problem. We show that it is possible to obtain a very good Ðt to the observed spectral line shapes by slightly changing the iron abundance (for both the LTE and NLTE cases). In general, the iron abundance we need for reaching the best NLTE Ðt to observed equivalent widths is 0.074^0.03 dex larger than that needed to obtain the best LTE Ðt. Our most relevant conclusion with regard to the solar iron abundance issue is the following : if NLTE e †ects are fully taken into account in the three-dimensional model of the solar photosphere, we obtain the meteoritic iron abundance value However, if the abundance analysis is done assuming LTE, (A Fe \ 7.50). we Ðnd in close agreement with the recent LTE analysis of Asplund and collaborators. A Fe \ 7.43, Our results do indicate that NLTE e †ects are signiÐcant but not above the 0.1 dex level in the Sun. We consider our NLTE result for the i...

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The Iron Line Formation Problem in Three‐dimensional Hydrodynamic Models of Solar‐like Photospheres

Shchukina

Bueno

2001

ApJ

157

197

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“…In this Letter, we carry out a three-dimensional radiative magnetohydrodynamic simulation of the solar wind formation starting from the solar upper convection zone. To emulate the small-scale dynamo and wave excitations near the photosphere, we extend the established convection model (Nordlund 1984;Stein & Nordlund 1998;Nordlund et al 2009), which is almost parameter free except the domain size or numerical resolution. This model has been extended to study the dynamics in the chromosphere and corona (Gudiksen et al 2011;Iijima & Yokoyama 2017;Rempel 2017).…”

Section: Introductionmentioning

confidence: 99%

A Comprehensive Simulation of Solar Wind Formation from the Solar Interior: Significant Cross-field Energy Transport by Interchange Reconnection near the Sun

Iijima

Matsumoto

Hotta

et al. 2023

ApJL

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The physical connection between thermal convection in the solar interior and the solar wind remains unclear due to their significant scale separation. Using an extended version of the three-dimensional radiative magnetohydrodynamic code RAMENS, we perform the first comprehensive simulation of the solar wind formation, starting from the wave excitation and the small-scale dynamo below the photosphere. The simulation satisfies various observational constraints as a slow solar wind emanating from the coronal hole boundary. The magnetic energy is persistently released in the simulated corona, showing a hot upward flow at the interface between open and closed fields. To evaluate the energetic contributions from Alfvén wave and interchange reconnection, we develop a new method to quantify the cross-field energy transport in the simulated atmosphere. The measured energy transport from closed coronal loops to open field accounts for approximately half of the total. These findings suggest a significant role of the supergranular-scale interchange reconnection in solar wind formation.

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NLTE Spectral Line Formation in Three Dimensions

Cited by 4 publications

References 4 publications

The Iron Line Formation Problem in Three‐dimensional Hydrodynamic Models of Solar‐like Photospheres

The Iron Line Formation Problem in Three‐dimensional Hydrodynamic Models of Solar‐like Photospheres

A Comprehensive Simulation of Solar Wind Formation from the Solar Interior: Significant Cross-field Energy Transport by Interchange Reconnection near the Sun

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