The Experts below are selected from a list of 243 Experts worldwide ranked by ideXlab platform
Javier Trujillo Bueno - One of the best experts on this subject based on the ideXlab platform.
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the polarization of the solar mg ii h and K Lines
The Astrophysical Journal, 2012Co-Authors: L Belluzzi, Javier Trujillo BuenoAbstract:Although the h and K Lines of Mg II are expected to be of great interest for probing the upper solar chromosphere, relatively little is Known about their polarization properties which encode the information on the magnetic field. Here we report the first results of an investigation whose main goal is to understand the physical mechanisms that control the scattering polarization across these resonance Lines and to achieve a realistic radiative transfer modeling in the presence of arbitrary magnetic fields. We show that the joint action of partial frequency redistribution (PRD) and quantum interference between the upper J-levels of the two Lines produces a complex fractional linear polarization (Q/I) pattern with large polarization amplitudes in the blue and red wings, and a negative feature in the spectral region between the two Lines. Another remarKable peculiarity of the Q/I profile is a conspicuous antisymmetric signal around the center of the h line, which cannot be obtained unless both PRD and J-state interference effects are taKen into account. In the core of the K line, PRD effects alone produce a triplet peaK structure in the Q/I profile, the modeling of which can also be achieved via the two-level atom approximation. In addition to the Hanle effect in the core of the K line, we also emphasize the diagnostic potential of the circular polarization produced by the Zeeman effect in the h and K Lines, as well as in other Mg II Lines located in their wings.
B De Pontieu - One of the best experts on this subject based on the ideXlab platform.
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the formation of iris diagnostics ii the formation of the mg ii h K Lines in the solar atmosphere
The Astrophysical Journal, 2013Co-Authors: Jorrit Leenaarts, M Carlsson, T M D Pereira, H Uitenbroek, B De PontieuAbstract:NASA's Interface Region Imaging Spectrograph (IRIS) small explorer mission will study how the solar atmosphere is energized. IRIS contains an imaging spectrograph that covers the Mg II h and K Lines as well as a slit-jaw imager centered at Mg II K. Understanding the observations requires forward modeling of Mg II h and K line formation from three-dimensional (3D) radiation-magnetohydrodynamic (RMHD) models. This paper is the second in a series where we undertaKe this modeling. We compute the vertically emergent h and K intensity from a snapshot of a dynamic 3D RMHD model of the solar atmosphere, and investigate which diagnostic information about the atmosphere is contained in the synthetic line profiles. We find that the Doppler shift of the central line depression correlates strongly with the vertical velocity at optical depth unity, which is typically located less than 200 Km below the transition region (TR). By combining the Doppler shifts of the h and K Lines we can retrieve the sign of the velocity gradient just below the TR. The intensity in the central line depression is anti-correlated with the formation height, especially in subfields of a few square Mm. This intensity could thus be used to measure themore » spatial variation of the height of the TR. The intensity in the line-core emission peaKs correlates with the temperature at its formation height, especially for strong emission peaKs. The peaKs can thus be exploited as a temperature diagnostic. The wavelength difference between the blue and red peaKs provides a diagnostic of the velocity gradients in the upper chromosphere. The intensity ratio of the blue and red peaKs correlates strongly with the average velocity in the upper chromosphere. We conclude that the Mg II h and K Lines are excellent probes of the very upper chromosphere just below the TR, a height regime that is impossible to probe with other spectral Lines. They also provide decent temperature and velocity diagnostics of the middle chromosphere.« less
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the formation of iris diagnostics i a quintessential model atom of mg ii and general formation properties of the mg ii h K Lines
The Astrophysical Journal, 2013Co-Authors: J Leenaarts, M Carlsson, T M D Pereira, H Uitenbroek, B De PontieuAbstract:NASA's Interface Region Imaging Spectrograph (IRIS) space mission will study how the solar atmosphere is energized. IRIS contains an imaging spectrograph that covers the Mg II h and K Lines as well as a slit-jaw imager centered at Mg II K. Understanding the observations will require forward modeling of Mg II h and K line formation from three-dimensional (3D) radiation-MHD models. This paper is the first in a series where we undertaKe this forward modeling. We discuss the atomic physics pertinent to h and K line formation, present a quintessential model atom that can be used in radiative transfer computations, and discuss the effect of partial redistribution (PRD) and 3D radiative transfer on the emergent line profiles. We conclude that Mg II h and K can be modeled accurately with a four-level plus continuum Mg II model atom. Ideally radiative transfer computations should be done in 3D including PRD effects. In practice this is currently not possible. A reasonable compromise is to use one-dimensional PRD computations to model the line profile up to and including the central emission peaKs, and use 3D transfer assuming complete redistribution to model the central depression.
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the formation of iris diagnostics ii the formation of the mg ii h K Lines in the solar atmosphere
arXiv: Solar and Stellar Astrophysics, 2013Co-Authors: Jorrit Leenaarts, M Carlsson, T M D Pereira, H Uitenbroek, B De PontieuAbstract:NASA's Interface Region Imaging Spectrograph (IRIS) small explorer mission will study how the solar atmosphere is energized. IRIS contains an imaging spectrograph that covers the Mg II h&K Lines as well as a slit-jaw imager centered at Mg II K. Understanding the observations requires forward modeling of Mg II h&K line formation from 3D radiation-MHD models. We compute the vertically emergent h&K intensity from a snapshot of a dynamic 3D radiation-MHD model of the solar atmosphere, and investigate which diagnostic information about the atmosphere is contained in the synthetic line profiles. We find that the Doppler shift of the central line depression correlates strongly with the vertical velocity at optical depth unity, which is typically located less than 200 Km below the transition region (TR). By combining the Doppler shifts of the h and the K line we can retrieve the sign of the velocity gradient just below the TR. The intensity in the central line depression is anticorrelated with the formation height, especially in subfields of a few square Mm. This intensity could thus be used to measure the spatial variation of the height of the transition region. The intensity in the line-core emission peaKs correlates with the temperature at its formation height, especially for strong emission peaKs. The peaKs can thus be exploited as a temperature diagnostic. The wavelength difference between the blue and red peaKs provides a diagnostic of the velocity gradients in the upper chromosphere. The intensity ratio of the blue and red peaKs correlates strongly with the average velocity in the upper chromosphere. We conclude that the Mg II h&K Lines are excellent probes of the very upper chromosphere just below the transition region, a height regime that is impossible to probe with other spectral Lines.
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the formation of iris diagnostics i a quintessential model atom of mg ii and general formation properties of the mg ii h K Lines
arXiv: Solar and Stellar Astrophysics, 2013Co-Authors: J Leenaarts, M Carlsson, T M D Pereira, H Uitenbroek, B De PontieuAbstract:NASA's Interface Region Imaging Spectrograph (IRIS) space mission will study how the solar atmosphere is energized. IRIS contains an imaging spectrograph that covers the Mg II h&K Lines as well as a slit-jaw imager centered at Mg II K. Understanding the observations will require forward modeling of Mg II h&K line formation from 3D radiation-MHD models. This paper is the first in a series where we undertaKe this forward modeling. We discuss the atomic physics pertinent to h&K line formation, present a quintessential model atom that can be used in radiative transfer computations and discuss the effect of partial redistribution (PRD) and 3D radiative transfer on the emergent line profiles. We conclude that Mg II h&K can be modeled accurately with a 4-level plus continuum Mg II model atom. Ideally radiative transfer computations should be done in 3D including PRD effects. In practice this is currently not possible. A reasonable compromise is to use 1D PRD computations to model the line profile up to and including the central emission peaKs, and use 3D transfer assuming complete redistribution to model the central depression.
T M D Pereira - One of the best experts on this subject based on the ideXlab platform.
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the formation of iris diagnostics ii the formation of the mg ii h K Lines in the solar atmosphere
The Astrophysical Journal, 2013Co-Authors: Jorrit Leenaarts, M Carlsson, T M D Pereira, H Uitenbroek, B De PontieuAbstract:NASA's Interface Region Imaging Spectrograph (IRIS) small explorer mission will study how the solar atmosphere is energized. IRIS contains an imaging spectrograph that covers the Mg II h and K Lines as well as a slit-jaw imager centered at Mg II K. Understanding the observations requires forward modeling of Mg II h and K line formation from three-dimensional (3D) radiation-magnetohydrodynamic (RMHD) models. This paper is the second in a series where we undertaKe this modeling. We compute the vertically emergent h and K intensity from a snapshot of a dynamic 3D RMHD model of the solar atmosphere, and investigate which diagnostic information about the atmosphere is contained in the synthetic line profiles. We find that the Doppler shift of the central line depression correlates strongly with the vertical velocity at optical depth unity, which is typically located less than 200 Km below the transition region (TR). By combining the Doppler shifts of the h and K Lines we can retrieve the sign of the velocity gradient just below the TR. The intensity in the central line depression is anti-correlated with the formation height, especially in subfields of a few square Mm. This intensity could thus be used to measure themore » spatial variation of the height of the TR. The intensity in the line-core emission peaKs correlates with the temperature at its formation height, especially for strong emission peaKs. The peaKs can thus be exploited as a temperature diagnostic. The wavelength difference between the blue and red peaKs provides a diagnostic of the velocity gradients in the upper chromosphere. The intensity ratio of the blue and red peaKs correlates strongly with the average velocity in the upper chromosphere. We conclude that the Mg II h and K Lines are excellent probes of the very upper chromosphere just below the TR, a height regime that is impossible to probe with other spectral Lines. They also provide decent temperature and velocity diagnostics of the middle chromosphere.« less
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the formation of iris diagnostics i a quintessential model atom of mg ii and general formation properties of the mg ii h K Lines
The Astrophysical Journal, 2013Co-Authors: J Leenaarts, M Carlsson, T M D Pereira, H Uitenbroek, B De PontieuAbstract:NASA's Interface Region Imaging Spectrograph (IRIS) space mission will study how the solar atmosphere is energized. IRIS contains an imaging spectrograph that covers the Mg II h and K Lines as well as a slit-jaw imager centered at Mg II K. Understanding the observations will require forward modeling of Mg II h and K line formation from three-dimensional (3D) radiation-MHD models. This paper is the first in a series where we undertaKe this forward modeling. We discuss the atomic physics pertinent to h and K line formation, present a quintessential model atom that can be used in radiative transfer computations, and discuss the effect of partial redistribution (PRD) and 3D radiative transfer on the emergent line profiles. We conclude that Mg II h and K can be modeled accurately with a four-level plus continuum Mg II model atom. Ideally radiative transfer computations should be done in 3D including PRD effects. In practice this is currently not possible. A reasonable compromise is to use one-dimensional PRD computations to model the line profile up to and including the central emission peaKs, and use 3D transfer assuming complete redistribution to model the central depression.
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the formation of iris diagnostics ii the formation of the mg ii h K Lines in the solar atmosphere
arXiv: Solar and Stellar Astrophysics, 2013Co-Authors: Jorrit Leenaarts, M Carlsson, T M D Pereira, H Uitenbroek, B De PontieuAbstract:NASA's Interface Region Imaging Spectrograph (IRIS) small explorer mission will study how the solar atmosphere is energized. IRIS contains an imaging spectrograph that covers the Mg II h&K Lines as well as a slit-jaw imager centered at Mg II K. Understanding the observations requires forward modeling of Mg II h&K line formation from 3D radiation-MHD models. We compute the vertically emergent h&K intensity from a snapshot of a dynamic 3D radiation-MHD model of the solar atmosphere, and investigate which diagnostic information about the atmosphere is contained in the synthetic line profiles. We find that the Doppler shift of the central line depression correlates strongly with the vertical velocity at optical depth unity, which is typically located less than 200 Km below the transition region (TR). By combining the Doppler shifts of the h and the K line we can retrieve the sign of the velocity gradient just below the TR. The intensity in the central line depression is anticorrelated with the formation height, especially in subfields of a few square Mm. This intensity could thus be used to measure the spatial variation of the height of the transition region. The intensity in the line-core emission peaKs correlates with the temperature at its formation height, especially for strong emission peaKs. The peaKs can thus be exploited as a temperature diagnostic. The wavelength difference between the blue and red peaKs provides a diagnostic of the velocity gradients in the upper chromosphere. The intensity ratio of the blue and red peaKs correlates strongly with the average velocity in the upper chromosphere. We conclude that the Mg II h&K Lines are excellent probes of the very upper chromosphere just below the transition region, a height regime that is impossible to probe with other spectral Lines.
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the formation of iris diagnostics i a quintessential model atom of mg ii and general formation properties of the mg ii h K Lines
arXiv: Solar and Stellar Astrophysics, 2013Co-Authors: J Leenaarts, M Carlsson, T M D Pereira, H Uitenbroek, B De PontieuAbstract:NASA's Interface Region Imaging Spectrograph (IRIS) space mission will study how the solar atmosphere is energized. IRIS contains an imaging spectrograph that covers the Mg II h&K Lines as well as a slit-jaw imager centered at Mg II K. Understanding the observations will require forward modeling of Mg II h&K line formation from 3D radiation-MHD models. This paper is the first in a series where we undertaKe this forward modeling. We discuss the atomic physics pertinent to h&K line formation, present a quintessential model atom that can be used in radiative transfer computations and discuss the effect of partial redistribution (PRD) and 3D radiative transfer on the emergent line profiles. We conclude that Mg II h&K can be modeled accurately with a 4-level plus continuum Mg II model atom. Ideally radiative transfer computations should be done in 3D including PRD effects. In practice this is currently not possible. A reasonable compromise is to use 1D PRD computations to model the line profile up to and including the central emission peaKs, and use 3D transfer assuming complete redistribution to model the central depression.
Yunping Zheng - One of the best experts on this subject based on the ideXlab platform.
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A Novel Gray Image Representation Method by Using Direct Non-symmetry and Anti-pacKing Model with K-Lines
2009 International Joint Conference on Artificial Intelligence, 2009Co-Authors: Wenming Yi, Renbin Xiao, Yunping ZhengAbstract:Although the image representation methods of the hierarchical data structures have many merits and applications, they put too much emphasis upon the symmetry of segmentation. Therefore, they are not the optimal representation methods. In this paper, we propose a novel gray image representation method by using the direct non-symmetry and anti-pacKing model with K-Lines (DNAMK). Also, we present an algorithm of the DNAMK for gray images and analyze the storage structure and the total data amount of the algorithm. By comparing the representation algorithm of the DNAMK with those of the triangle non-symmetry and anti-pacKing model (TNAM) and the classic linear quadtree, the experimental results presented in this paper show that the former can greatly reduce the numbers of subpatterns or nodes and simultaneously save the data storage much more effectively than the latter, and therefore it is a better method to represent gray images.
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JCAI - A Novel Gray Image Representation Method by Using Direct Non-symmetry and Anti-pacKing Model with K-Lines
2009 International Joint Conference on Artificial Intelligence, 2009Co-Authors: Wenming Yi, Renbin Xiao, Yunping ZhengAbstract:Although the image representation methods of the hierarchical data structures have many merits and applications, they put too much emphasis upon the symmetry of segmentation. Therefore, they are not the optimal representation methods. In this paper, we propose a novel gray image representation method by using the direct non-symmetry and anti-pacKing model with K-Lines (DNAMK). Also, we present an algorithm of the DNAMK for gray images and analyze the storage structure and the total data amount of the algorithm. By comparing the representation algorithm of the DNAMK with those of the triangle non-symmetry and anti-pacKing model (TNAM) and the classic linear quadtree, the experimental results presented in this paper show that the former can greatly reduce the numbers of subpatterns or nodes and simultaneously save the data storage much more effectively than the latter, and therefore it is a better method to represent gray images.
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A Novel Algorithm Using Non-symmetry and Anti-pacKing Model with K-Lines for Binary Image Representation
2008 Congress on Image and Signal Processing, 2008Co-Authors: Yunping Zheng, Chuanbo Chen, Mudar SaremAbstract:In this paper, we propose a novel algorithm using the NAMK (Non-symmetry and Anti-pacKing pattern representation Model with K-Lines) for the binary image representation. By comparing the algorithm using the NAMK with that using the popular linear quadtree, the theoretical and experimental results presented in this paper show that the former can reduce the data storage much more effectively than the latter and it is a better method to represent the binary image. The algorithm using the NAMK for the binary image representation presented in this paper is valuable for the theoretical research and potential business foregrounds such as decreasing the storage space, increasing the transmission speed, quicKening the process procedure, and so forth.
M Carlsson - One of the best experts on this subject based on the ideXlab platform.
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three dimensional modeling of the ca ii h and K Lines in the solar atmosphere
Astronomy and Astrophysics, 2018Co-Authors: Johan P Bjorgen, Andrii V Sukhorukov, Jorrit Leenaarts, M Carlsson, Jaime De La Cruz Rodriguez, G B Scharmer, V H HansteenAbstract:Context. CHROMIS, a new imaging spectrometer at the Swedish 1-m Solar Telescope (SST), can observe the chromosphere in the H and K Lines of Ca II at high spatial and spectral resolution. Accurate m ...
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the formation of iris diagnostics ii the formation of the mg ii h K Lines in the solar atmosphere
The Astrophysical Journal, 2013Co-Authors: Jorrit Leenaarts, M Carlsson, T M D Pereira, H Uitenbroek, B De PontieuAbstract:NASA's Interface Region Imaging Spectrograph (IRIS) small explorer mission will study how the solar atmosphere is energized. IRIS contains an imaging spectrograph that covers the Mg II h and K Lines as well as a slit-jaw imager centered at Mg II K. Understanding the observations requires forward modeling of Mg II h and K line formation from three-dimensional (3D) radiation-magnetohydrodynamic (RMHD) models. This paper is the second in a series where we undertaKe this modeling. We compute the vertically emergent h and K intensity from a snapshot of a dynamic 3D RMHD model of the solar atmosphere, and investigate which diagnostic information about the atmosphere is contained in the synthetic line profiles. We find that the Doppler shift of the central line depression correlates strongly with the vertical velocity at optical depth unity, which is typically located less than 200 Km below the transition region (TR). By combining the Doppler shifts of the h and K Lines we can retrieve the sign of the velocity gradient just below the TR. The intensity in the central line depression is anti-correlated with the formation height, especially in subfields of a few square Mm. This intensity could thus be used to measure themore » spatial variation of the height of the TR. The intensity in the line-core emission peaKs correlates with the temperature at its formation height, especially for strong emission peaKs. The peaKs can thus be exploited as a temperature diagnostic. The wavelength difference between the blue and red peaKs provides a diagnostic of the velocity gradients in the upper chromosphere. The intensity ratio of the blue and red peaKs correlates strongly with the average velocity in the upper chromosphere. We conclude that the Mg II h and K Lines are excellent probes of the very upper chromosphere just below the TR, a height regime that is impossible to probe with other spectral Lines. They also provide decent temperature and velocity diagnostics of the middle chromosphere.« less
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the formation of iris diagnostics i a quintessential model atom of mg ii and general formation properties of the mg ii h K Lines
The Astrophysical Journal, 2013Co-Authors: J Leenaarts, M Carlsson, T M D Pereira, H Uitenbroek, B De PontieuAbstract:NASA's Interface Region Imaging Spectrograph (IRIS) space mission will study how the solar atmosphere is energized. IRIS contains an imaging spectrograph that covers the Mg II h and K Lines as well as a slit-jaw imager centered at Mg II K. Understanding the observations will require forward modeling of Mg II h and K line formation from three-dimensional (3D) radiation-MHD models. This paper is the first in a series where we undertaKe this forward modeling. We discuss the atomic physics pertinent to h and K line formation, present a quintessential model atom that can be used in radiative transfer computations, and discuss the effect of partial redistribution (PRD) and 3D radiative transfer on the emergent line profiles. We conclude that Mg II h and K can be modeled accurately with a four-level plus continuum Mg II model atom. Ideally radiative transfer computations should be done in 3D including PRD effects. In practice this is currently not possible. A reasonable compromise is to use one-dimensional PRD computations to model the line profile up to and including the central emission peaKs, and use 3D transfer assuming complete redistribution to model the central depression.
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the formation of iris diagnostics ii the formation of the mg ii h K Lines in the solar atmosphere
arXiv: Solar and Stellar Astrophysics, 2013Co-Authors: Jorrit Leenaarts, M Carlsson, T M D Pereira, H Uitenbroek, B De PontieuAbstract:NASA's Interface Region Imaging Spectrograph (IRIS) small explorer mission will study how the solar atmosphere is energized. IRIS contains an imaging spectrograph that covers the Mg II h&K Lines as well as a slit-jaw imager centered at Mg II K. Understanding the observations requires forward modeling of Mg II h&K line formation from 3D radiation-MHD models. We compute the vertically emergent h&K intensity from a snapshot of a dynamic 3D radiation-MHD model of the solar atmosphere, and investigate which diagnostic information about the atmosphere is contained in the synthetic line profiles. We find that the Doppler shift of the central line depression correlates strongly with the vertical velocity at optical depth unity, which is typically located less than 200 Km below the transition region (TR). By combining the Doppler shifts of the h and the K line we can retrieve the sign of the velocity gradient just below the TR. The intensity in the central line depression is anticorrelated with the formation height, especially in subfields of a few square Mm. This intensity could thus be used to measure the spatial variation of the height of the transition region. The intensity in the line-core emission peaKs correlates with the temperature at its formation height, especially for strong emission peaKs. The peaKs can thus be exploited as a temperature diagnostic. The wavelength difference between the blue and red peaKs provides a diagnostic of the velocity gradients in the upper chromosphere. The intensity ratio of the blue and red peaKs correlates strongly with the average velocity in the upper chromosphere. We conclude that the Mg II h&K Lines are excellent probes of the very upper chromosphere just below the transition region, a height regime that is impossible to probe with other spectral Lines.
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the formation of iris diagnostics i a quintessential model atom of mg ii and general formation properties of the mg ii h K Lines
arXiv: Solar and Stellar Astrophysics, 2013Co-Authors: J Leenaarts, M Carlsson, T M D Pereira, H Uitenbroek, B De PontieuAbstract:NASA's Interface Region Imaging Spectrograph (IRIS) space mission will study how the solar atmosphere is energized. IRIS contains an imaging spectrograph that covers the Mg II h&K Lines as well as a slit-jaw imager centered at Mg II K. Understanding the observations will require forward modeling of Mg II h&K line formation from 3D radiation-MHD models. This paper is the first in a series where we undertaKe this forward modeling. We discuss the atomic physics pertinent to h&K line formation, present a quintessential model atom that can be used in radiative transfer computations and discuss the effect of partial redistribution (PRD) and 3D radiative transfer on the emergent line profiles. We conclude that Mg II h&K can be modeled accurately with a 4-level plus continuum Mg II model atom. Ideally radiative transfer computations should be done in 3D including PRD effects. In practice this is currently not possible. A reasonable compromise is to use 1D PRD computations to model the line profile up to and including the central emission peaKs, and use 3D transfer assuming complete redistribution to model the central depression.
