The Experts below are selected from a list of 231 Experts worldwide ranked by ideXlab platform
Sarbani Basu - One of the best experts on this subject based on the ideXlab platform.
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Helioseismology and Solar Abundances
Physics Reports, 2020Co-Authors: Sarbani Basu, H M AntiaAbstract:Helioseismology has allowed us to study the structure of the Sun in unprecedented detail. One of the triumphs of the theory of stellar evolution was that helioseismic studies had shown that the structure of Solar models is very similar to that of the Sun. However, this agreement has been spoiled by recent revisions of the Solar heavy-element Abundances. Heavy element Abundances determine the opacity of the stellar material and hence, are an important input to stellar model calculations. The models with the new, low Abundances do not satisfy helioseismic constraints. We review here how heavy-element Abundances affect Solar models, how these models are tested with helioseismology, and the impact of the new Abundances on standard Solar models. We also discuss the attempts made to improve the agreement of the low-abundance models with the Sun and discuss how helioseismology is being used to determine the Solar heavy-element abundance. A review of current literature shows that attempts to improve agreement between Solar models with low heavy-element Abundances and seismic inference have been unsuccessful so far. The low-metallicity models that have the least disagreement with seismic data require changing all input physics to stellar models beyond their acceptable ranges. Seismic determinations of the Solar heavy-element abundance yield results that are consistent with the older, higher values of the Solar abundance, and hence, no major changes to the inputs to Solar models are required to make higher-metallicity Solar models consistent with helioseismic data.Comment: To appear in Physics Reports. Large file (1.6M PDF, 3.4M PS), 27 figure
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revisiting the issue of Solar Abundances
Journal of Physics: Conference Series, 2013Co-Authors: Sarbani Basu, H M AntiaAbstract:We revisit the issue of Solar Abundances and examine whether the updated Abundances result in Solar models that have structures that agree with the structure of the Sun as determined by helioseismology. We quantify the changes in opacity required to bring the models constructed with the newer Solar Abundances in agreement with the Sun.
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are recent Solar heavy element Abundances consistent with helioseismology
GONG-SoHO 24: A New Era of Seismology of the Sun and Solar-Like Stars, 2011Co-Authors: H M Antia, Sarbani BasuAbstract:During the last decade the Abundances of heavy elements in the Sun have been revised downwards leading to serious discrepancy between Solar models constructed using these Abundances and the available seismic data. Much of these downward revision of Abundances of Oxygen and other light elements was attributed to use of improved 3D Solar atmospheric models. Recently, independent 3D models have been used to calculate Solar Abundances of these elements and calculated values are higher than the earlier estimates also obtained using 3D atmospheric models. In this work we investigate if these revised Abundances are consistent with seismic data. We also investigate whether an increase in Neon abundance can help in resolving the discrepancy.
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New Solar composition: the problem with Solar models revisited
The Astrophysical Journal, 2009Co-Authors: Aldo Serenelli, Sarbani Basu, Jason W. Ferguson, Martin AsplundAbstract:We construct updated Solar models with different sets of Solar Abundances, including the most recent determinations by Asplund et al. The latter work predicts a larger (~10%) Solar metallicity compared to previous measurements by the same authors but significantly lower (~25%) than the recommended value from a decade ago by Grevesse & Sauval. We compare the results of our models with determinations of the Solar structure inferred through helioseismology measurements. The model that uses the most recent Solar abundance determinations predicts the base of the Solar convective envelope to be located at R CZ = 0.724 R ☉ and a surface helium mass fraction of Y surf = 0.231. These results are in conflict with helioseismology data (R CZ = 0.713 ± 0.001 R ☉ and Y surf = 0.2485 ± 0.0035) at 5σ and 11σ levels, respectively. Using the new Solar Abundances, we calculate the magnitude by which radiative opacities should be modified in order to restore agreement with helioseismology. We find that a maximum change of ~15% at the base of the convective zone is required with a smooth decrease toward the core, where the change needed is ~5%. The required change at the base of the convective envelope is about half the value estimated previously. We also present the Solar neutrino fluxes predicted by the new models. The most important changes brought about by the new Solar Abundances are the increase by ~10% in the predicted 13N and 15O fluxes that arise mostly due to the increase in the C and N Abundances in the newly determined Solar composition.
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helioseismology and Solar Abundances
Physics Reports, 2008Co-Authors: Sarbani Basu, H M AntiaAbstract:Helioseismology has allowed us to study the structure of the Sun in unprecedented detail. One of the triumphs of the theory of stellar evolution was that helioseismic studies had shown that the structure of Solar models is very similar to that of the Sun. However, this agreement has been spoiled by recent revisions of the Solar heavy-element Abundances. Heavy-element Abundances determine the opacity of the stellar material and hence, are an important input to stellar model calculations. The models with the new, low Abundances do not satisfy helioseismic constraints. We review here how heavy-element Abundances affect Solar models, how these models are tested with helioseismology, and the impact of the new Abundances on standard Solar models. We also discuss the attempts made to improve the agreement of the low-abundance models with the Sun and discuss how helioseismology is being used to determine the Solar heavy-element Abundances. A review of current literature shows that attempts to improve agreement between Solar models with low heavy-element Abundances and seismic inference have been unsuccessful so far. The low-metallicity models that have the least disagreement with seismic data require changing all input physics to stellar models beyond their acceptable ranges. Seismic determinations of the Solar heavy-element Abundances yield results that are consistent with the older, higher values of the Solar abundance, and hence, no major changes to the inputs to Solar models are required to make higher-metallicity Solar models consistent with the helioseismic data.
H M Antia - One of the best experts on this subject based on the ideXlab platform.
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Helioseismology and Solar Abundances
Physics Reports, 2020Co-Authors: Sarbani Basu, H M AntiaAbstract:Helioseismology has allowed us to study the structure of the Sun in unprecedented detail. One of the triumphs of the theory of stellar evolution was that helioseismic studies had shown that the structure of Solar models is very similar to that of the Sun. However, this agreement has been spoiled by recent revisions of the Solar heavy-element Abundances. Heavy element Abundances determine the opacity of the stellar material and hence, are an important input to stellar model calculations. The models with the new, low Abundances do not satisfy helioseismic constraints. We review here how heavy-element Abundances affect Solar models, how these models are tested with helioseismology, and the impact of the new Abundances on standard Solar models. We also discuss the attempts made to improve the agreement of the low-abundance models with the Sun and discuss how helioseismology is being used to determine the Solar heavy-element abundance. A review of current literature shows that attempts to improve agreement between Solar models with low heavy-element Abundances and seismic inference have been unsuccessful so far. The low-metallicity models that have the least disagreement with seismic data require changing all input physics to stellar models beyond their acceptable ranges. Seismic determinations of the Solar heavy-element abundance yield results that are consistent with the older, higher values of the Solar abundance, and hence, no major changes to the inputs to Solar models are required to make higher-metallicity Solar models consistent with helioseismic data.Comment: To appear in Physics Reports. Large file (1.6M PDF, 3.4M PS), 27 figure
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revisiting the issue of Solar Abundances
Journal of Physics: Conference Series, 2013Co-Authors: Sarbani Basu, H M AntiaAbstract:We revisit the issue of Solar Abundances and examine whether the updated Abundances result in Solar models that have structures that agree with the structure of the Sun as determined by helioseismology. We quantify the changes in opacity required to bring the models constructed with the newer Solar Abundances in agreement with the Sun.
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are recent Solar heavy element Abundances consistent with helioseismology
GONG-SoHO 24: A New Era of Seismology of the Sun and Solar-Like Stars, 2011Co-Authors: H M Antia, Sarbani BasuAbstract:During the last decade the Abundances of heavy elements in the Sun have been revised downwards leading to serious discrepancy between Solar models constructed using these Abundances and the available seismic data. Much of these downward revision of Abundances of Oxygen and other light elements was attributed to use of improved 3D Solar atmospheric models. Recently, independent 3D models have been used to calculate Solar Abundances of these elements and calculated values are higher than the earlier estimates also obtained using 3D atmospheric models. In this work we investigate if these revised Abundances are consistent with seismic data. We also investigate whether an increase in Neon abundance can help in resolving the discrepancy.
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helioseismology and Solar Abundances
Physics Reports, 2008Co-Authors: Sarbani Basu, H M AntiaAbstract:Helioseismology has allowed us to study the structure of the Sun in unprecedented detail. One of the triumphs of the theory of stellar evolution was that helioseismic studies had shown that the structure of Solar models is very similar to that of the Sun. However, this agreement has been spoiled by recent revisions of the Solar heavy-element Abundances. Heavy-element Abundances determine the opacity of the stellar material and hence, are an important input to stellar model calculations. The models with the new, low Abundances do not satisfy helioseismic constraints. We review here how heavy-element Abundances affect Solar models, how these models are tested with helioseismology, and the impact of the new Abundances on standard Solar models. We also discuss the attempts made to improve the agreement of the low-abundance models with the Sun and discuss how helioseismology is being used to determine the Solar heavy-element Abundances. A review of current literature shows that attempts to improve agreement between Solar models with low heavy-element Abundances and seismic inference have been unsuccessful so far. The low-metallicity models that have the least disagreement with seismic data require changing all input physics to stellar models beyond their acceptable ranges. Seismic determinations of the Solar heavy-element Abundances yield results that are consistent with the older, higher values of the Solar abundance, and hence, no major changes to the inputs to Solar models are required to make higher-metallicity Solar models consistent with the helioseismic data.
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determining Solar Abundances using helioseismology
The Astrophysical Journal, 2006Co-Authors: H M Antia, Sarbani BasuAbstract:The recent downward revision of Solar photospheric Abundances of oxygen and other heavy elements has resulted in serious discrepancies between Solar models and Solar structure as determined through helioseismology. In this work we investigate the possibility of determining the Solar heavy-element abundance without reference to spectroscopy by using helioseismic data. Using the dimensionless sound-speed derivative in the Solar convection zone, we find that the heavy-element abundance Z = 0.0172 ± 0.002, which is closer to the older, higher value of the Abundances.
Piercarlo Bonifacio - One of the best experts on this subject based on the ideXlab platform.
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Solar Chemical Abundances Determined with a CO5BOLD 3D Model Atmosphere
Solar Physics, 2011Co-Authors: E Caffau, Bernd Freytag, H G Ludwig, M. Steffen, Piercarlo BonifacioAbstract:In the last decade, the photospheric Solar metallicity as determined from spectroscopy experienced a remarkable downward revision. Part of this effect can be attributed to an improvement of atomic data and the inclusion of NLTE computations, but also the use of hydrodynamical model atmospheres seemed to play a role. This “decrease” with time of the metallicity of the Solar photosphere increased the disagreement with the results from helioseismology. With a CO ^5 BOLD 3D model of the Solar atmosphere, the CIFIST team at the Paris Observatory re-determined the photospheric Solar Abundances of several elements, among them C, N, and O. The spectroscopic Abundances are obtained by fitting the equivalent width and/or the profile of observed spectral lines with synthetic spectra computed from the 3D model atmosphere. We conclude that the effects of granular fluctuations depend on the characteristics of the individual lines, but are found to be relevant only in a few particular cases. 3D effects are not responsible for the systematic lowering of the Solar Abundances in recent years. The Solar metallicity resulting from this analysis is Z =0.0153, Z / X =0.0209.
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Solar chemical Abundances determined with a co5bold 3d model atmosphere
Solar Physics, 2011Co-Authors: E Caffau, Matthias Steffen, Bernd Freytag, H G Ludwig, Piercarlo BonifacioAbstract:In the last decade, the photospheric Solar metallicity as determined from spectroscopy experienced a remarkable downward revision. Part of this effect can be attributed to an improvement of atomic data and the inclusion of NLTE computations, but also the use of hydrodynamical model atmospheres seemed to play a role. This ``decrease'' with time of the metallicity of the Solar photosphere increased the disagreement with the results from helioseismology. With a CO5BOLD 3D model of the Solar atmosphere, the CIFIST team at the Paris Observatory re-determined the photospheric Solar Abundances of several elements, among them C, N, and O. The spectroscopic Abundances are obtained by fitting the equivalent width and/or the profile of observed spectral lines with synthetic spectra computed from the 3D model atmosphere. We conclude that the effects of granular fluctuations depend on the characteristics of the individual lines, but are found to be relevant only in a few particular cases. 3D effects are not reponsible for the systematic lowering of the Solar Abundances in recent years. The Solar metallicity resulting from this analysis is Z=0.0153, Z/X=0.0209.
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Solar Abundances and 3D model atmospheres
arXiv: Solar and Stellar Astrophysics, 2009Co-Authors: H. G. Ludwig, Elisabetta Caffau, Matthias Steffen, Piercarlo Bonifacio, Bernd Freytag, Roger CayrelAbstract:We present Solar photospheric Abundances for 12 elements from optical and near-infrared spectroscopy. The abundance analysis was conducted employing 3D hydrodynamical ( CO 5 BOLD ) as well as standard 1D hydrostatic model atmospheres. We compare our results to others with emphasis on discrepancies and still lingering problems, in particular exemplified by the pivotal abundance of oxygen. We argue that the thermal structure of the lower Solar photosphere is very well represented by our 3D model. We obtain an excellent match of the observed center-to-limb variation of the line-blanketed continuum intensity, also at wavelengths shortward of the Balmer jump.
Sam M Austin - One of the best experts on this subject based on the ideXlab platform.
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on the sensitivity of massive star nucleosynthesis and evolution to Solar Abundances and to uncertainties in helium burning reaction rates
The Astrophysical Journal, 2007Co-Authors: Alexander Heger, Sam M AustinAbstract:We explore the dependence of presupernova evolution and supernova nucleosynthesis yields on the uncertainties in helium-burning reaction rates. Using the revised Solar Abundances of Lodders for the initial stellar composition, instead of those of Anders and Grevesse, changes the supernova yields and limits the constraints that those yields place on the 12C(α,γ)16O reaction rate. The production factors of medium-weight elements (A = 16-40) were found to be in reasonable agreement with observed Solar ratios within the current experimental uncertainties in the triple-α reaction rate. Simultaneous variations by the same amount in both reaction rates or in either of them separately, however, can induce significant changes in the central 12C abundance at core carbon ignition and in the mass of the supernova remnant. It therefore remains important to have experimental determinations of the helium-burning rates so that their ratio and absolute values are known with an accuracy of 10% or better.
Alexander Heger - One of the best experts on this subject based on the ideXlab platform.
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on the sensitivity of massive star nucleosynthesis and evolution to Solar Abundances and to uncertainties in helium burning reaction rates
The Astrophysical Journal, 2007Co-Authors: Alexander Heger, Sam M AustinAbstract:We explore the dependence of presupernova evolution and supernova nucleosynthesis yields on the uncertainties in helium-burning reaction rates. Using the revised Solar Abundances of Lodders for the initial stellar composition, instead of those of Anders and Grevesse, changes the supernova yields and limits the constraints that those yields place on the 12C(α,γ)16O reaction rate. The production factors of medium-weight elements (A = 16-40) were found to be in reasonable agreement with observed Solar ratios within the current experimental uncertainties in the triple-α reaction rate. Simultaneous variations by the same amount in both reaction rates or in either of them separately, however, can induce significant changes in the central 12C abundance at core carbon ignition and in the mass of the supernova remnant. It therefore remains important to have experimental determinations of the helium-burning rates so that their ratio and absolute values are known with an accuracy of 10% or better.