The Experts below are selected from a list of 186 Experts worldwide ranked by ideXlab platform
Ilídio Lopes - One of the best experts on this subject based on the ideXlab platform.
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The Impact of Composition Choices on Solar Evolution: Age, Helio– and Asteroseismology, and Neutrinos
Monthly Notices of the Royal Astronomical Society, 2020Co-Authors: Diogo Capelo, Ilídio LopesAbstract:The Sun is the most studied and well-known star, and as such, Solar fundamental parameters are often used to bridge gaps in the knowledge of other stars, when these are required for modelling. However, the two most powerful and precise independent methodologies currently available to infer the internal Solar structure are in disagreement. We aim to show the potential impact of composition choices in the overall Evolution of a star, using the Sun as an example. To this effect, we create two Standard Solar Models and a comparison model using different combinations of metallicity and relative element abundances and compare Evolutionary, helioseismic, and neutrino-related properties for each. We report differences in age for models calibrated to the same point in the HR diagram, in the red giant branch, of more than 1 Gyr, and found that the current precision level of asteroseismic measurements is enough to differentiate these models, which would exhibit differences in priod spacing of 1.30-2.58 per cent. Additionally, we show that the measurement of neutrino fluxes from the carbon-nitrogen-oxygen cycle with a precision of around 17 per cent, which could be achieved by the next generation of Solar neutrino experiments, could help resolve the stellar abundance problem.
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A First Estimation of the Last 7000 Years of Solar Evolution
AIP Conference Proceedings, 2007Co-Authors: Ilídio Lopes, Dário PassosAbstract:In order to understand the structural Evolution of the sun during the last seven millenia we have studied and analysed the Evolution of Solar luminosity obtained from a carbon‐14 proxy. From the obtained luminosity distribution, we found that the mean luminosity is 0.12%–0.14% lower that the adopted luminosity value used on the standard Solar model. The large standard deviation of the luminosity distribution of the Sun reveals a more active Evolution of the Sun than previously expected. Furthermore, we have studying the Sun Evolution model's response to this luminosity variations under several Evolution scenarios.
Pierre Demarque - One of the best experts on this subject based on the ideXlab platform.
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Helioseismology, Solar Evolution and other physics
Highlights of Astronomy, 1995Co-Authors: Pierre Demarque, Brian Chaboyer, D. B. Guenther, Marc H. PinsonneaultAbstract:The last few years have seen rapid progress in Solar interior modeling, and standard Solar models (SSM) now predict a p-mode oscillation spectrum which agrees, within the estimated uncertainties in the physical input, with the observed oscillation spectrum of the Sun (Guenther et al. , 1992a, 1992b; Guzik & Cox, 1993). This is the result of a number of improvements in the input physics, most notably the advances in opacities for the Solar interior (Rogers & Iglesias, 1994) and the low temperature regions of the Sun (Kurucz, 1991). The agreement between the observed Solar p-mode frequencies and the frequencies predicted by the SSM is not yet perfect, however, and understanding these discrepancies has become a focus of our research.
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ROTATION, DIFFUSION, AND OVERSHOOT IN THE SUN: EFFECTS ON THE OSCILLATION FREQUENCIES AND THE NEUTRINO FLUX
The Astrophysical Journal, 1995Co-Authors: Brian Chaboyer, Pierre Demarque, David B. Guenther, Marc H. PinsonneaultAbstract:We have studied the importance of the combined effects of rotation, diffusion, and convective overshoot on the p-mode oscillation spectrum and the neutrino flux of the standard Solar model. To isolate the various physical affects included in the new rotation plus diffusion models we also constructed Solar models to test the significance of diffusion and of overshoot by themselves. In previous studies, models that include helium diffusion during Solar Evolution were found to improve the predicted p-mode frequencies for some modes and worsen the agreement for others (Guenther \ea 1993). Here we verify this result for both the Bahcall and Loeb (1990) formulation of diffusion and the Proffitt and Michaud (1991) formulation of diffusion. We find that the effects of rotation on the Sun's structure in the outer layers perturbs the $p$-mode frequencies only slightly when compared to the more substantial effects due to diffusion. In the thin overshoot layer (taken here to be $0.1\, H_p$), we have compared the effect of overmixing in a radiative layer versus convective (adiabatic) penetration. Neither radiative overmixing nor adiabatic penetration has any significant effect on the $p$-modes, probably in part because the overshoot layer is constrained to be thin. The predicted neutrino flux in our diffusion plus rotation model is 7.12 SNU for Cl detectors, 127 SNU for Ga detectors and $5.00\times 10^6\,{\rm erg \, cm^{-2} }$ for the $^8$B neutrinos; this is approximately half-way between the standard Solar model without diffusion, and the standard Solar model with diffusion alone.
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The Sun as a probe of varying G
The Astrophysical Journal, 1994Co-Authors: Pierre Demarque, David B. Guenther, Lawrence M. Krauss, David NydamAbstract:In order to explore the ability of helioseismology and features of Solar models to test the constancy of the gravitational constant G during the last 4.5 Gyr of Solar Evolution, we have constructed a grid of Evolutionary sequences for Solar models under the assumptions that G varies with time, and have explored the sensitivity of their nonradial acoustic mode oscillation spectra to G variability. All final models satisfy the standard constraints for the present Sun and, except for the variation in G, were constructed under the assumptions of a standard Solar model. When compared with the observed Solar p-mode spectrum, our models definitely rule out beta greater than 0.4 and beta less than -0.4, where G(t) proportional to t(exp -beta) over the last 4.5 Gyr. These limits can be tightened to rule out absolute value of beta greater than 0 (0.1) by the use of other Solar observables. For nonmonotonic variation in G this suggests that long-timescale variations greater than 0 (5%) in G are ruled out over the last 4.5 Gyr. Future prospects for improving the sensitivity of helioseismic tests of a varying G are also discussed. Finally, we explore the sensitivity of the predicted Solar neutrino flux to varying G.
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Post-main-sequence Solar Evolution
1991Co-Authors: Pierre Demarque, David B. GuentherAbstract:The standard Evolution of a 1-Solar-mass star from the zero-age main sequence to the helium flash is discussed. Two areas of Solar-stellar research are examined which are presently in a state of rapid development: the theory of Solar and stellar nonradial acoustic (p-mode) oscillations, which can be used to test the pressure stratification in the stellar interior; and the theory of the Evolution of rotating stars, which predicts the Evolution of surface rotational velocities and the mixing of chemical elements to the surface. Oscillations and rotation are closely interrelated because each individual p-mode is also split in frequency by internal rotation in the region through which it propagates. Observations of p-mode splittings can provide information on the state of rotation of the Solar and stellar interiors.
Jean-paul Zahn - One of the best experts on this subject based on the ideXlab platform.
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Influence of the Tachocline on Solar Evolution
Annals of the New York Academy of Sciences, 2006Co-Authors: Allan Sacha Brun, Jean-paul ZahnAbstract:Recently helioseismic observations have revealed the presence of a shear layer at the base of the convective zone related to the transition from differential rotation in the convection zone to almost uniform rotation in the radiative interior, the tachocline. At present, this layer extends only over a few percent of the Solar radius and no definitive explanations have been given for this thiness. Following Spiegel and Zahn (1992, Astron. Astrophys.), who invoke anisotropic turbulence to stop the spread of the tachocline deeper in the radiative zone as the Sun evolves, we give some justifications for their hypothesis by taking into account recent results on rotating shear instability (Richard and Zahn 1999, Astron. Astrophys.). We study the impact of the macroscopic motions present in this layer on the Sun's structure and Evolution by introducing a macroscopic diffusivity $D_T$ in updated Solar models. We find that a time dependent treatment of the tachocline significantly improves the agreement between computed and observed surface chemical species, such as the $^7$Li and modify the internal structure of the Sun (Brun, Turck-Chi\`eze and Zahn, 1999, in Astrophys. J.).
Marc H. Pinsonneault - One of the best experts on this subject based on the ideXlab platform.
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Helioseismology, Solar Evolution and other physics
Highlights of Astronomy, 1995Co-Authors: Pierre Demarque, Brian Chaboyer, D. B. Guenther, Marc H. PinsonneaultAbstract:The last few years have seen rapid progress in Solar interior modeling, and standard Solar models (SSM) now predict a p-mode oscillation spectrum which agrees, within the estimated uncertainties in the physical input, with the observed oscillation spectrum of the Sun (Guenther et al. , 1992a, 1992b; Guzik & Cox, 1993). This is the result of a number of improvements in the input physics, most notably the advances in opacities for the Solar interior (Rogers & Iglesias, 1994) and the low temperature regions of the Sun (Kurucz, 1991). The agreement between the observed Solar p-mode frequencies and the frequencies predicted by the SSM is not yet perfect, however, and understanding these discrepancies has become a focus of our research.
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ROTATION, DIFFUSION, AND OVERSHOOT IN THE SUN: EFFECTS ON THE OSCILLATION FREQUENCIES AND THE NEUTRINO FLUX
The Astrophysical Journal, 1995Co-Authors: Brian Chaboyer, Pierre Demarque, David B. Guenther, Marc H. PinsonneaultAbstract:We have studied the importance of the combined effects of rotation, diffusion, and convective overshoot on the p-mode oscillation spectrum and the neutrino flux of the standard Solar model. To isolate the various physical affects included in the new rotation plus diffusion models we also constructed Solar models to test the significance of diffusion and of overshoot by themselves. In previous studies, models that include helium diffusion during Solar Evolution were found to improve the predicted p-mode frequencies for some modes and worsen the agreement for others (Guenther \ea 1993). Here we verify this result for both the Bahcall and Loeb (1990) formulation of diffusion and the Proffitt and Michaud (1991) formulation of diffusion. We find that the effects of rotation on the Sun's structure in the outer layers perturbs the $p$-mode frequencies only slightly when compared to the more substantial effects due to diffusion. In the thin overshoot layer (taken here to be $0.1\, H_p$), we have compared the effect of overmixing in a radiative layer versus convective (adiabatic) penetration. Neither radiative overmixing nor adiabatic penetration has any significant effect on the $p$-modes, probably in part because the overshoot layer is constrained to be thin. The predicted neutrino flux in our diffusion plus rotation model is 7.12 SNU for Cl detectors, 127 SNU for Ga detectors and $5.00\times 10^6\,{\rm erg \, cm^{-2} }$ for the $^8$B neutrinos; this is approximately half-way between the standard Solar model without diffusion, and the standard Solar model with diffusion alone.
Georg G. Raffelt - One of the best experts on this subject based on the ideXlab platform.
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Window for the dark matter solution to the Solar neutrino problem
The Astrophysical Journal, 1991Co-Authors: David S. P. Dearborn, Kim Griest, Georg G. RaffeltAbstract:The existence of dark matter particles (cosmions) inside the Sun has been suggested as an explanation for the disagreement between measured and theorical Solar neutrino fluxes. The new theorical results on cosmion capture, evaporation and energy tranport, as well as a modern Solar Evolution code, are used to estimate accuratly the range of cosmion masses and cross sections which can solve the Solar neutrino problem. A range somewhat smaller than previously estimated is found. Including new results from a silicon direct detection experiment, only two extremely small regions of parameter space remain acceptable for the coherent spin-independent cross sections often discussed.