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  • SOLAR PHYSICS  (8)
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  • 1
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    Is the Sun really a rigid rotator (1988)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: Attention is drawn to observations of surface rotational bands in subgiants which indicate that a deep-seated reservoir of angular momentum must exist in these stars. This interpretation is compatible with theoretical studies of the rotational history of the Sun and Sun-like stars, but is in conflict with observations of p-mode splittings in the Sun. In order to understand better the source of this discrepancy, the predicted rotational splittings of several test rotation curves are compared to solar data.
    Keywords: SOLAR PHYSICS
    Type: ESA, Seismology of the Sun and Sun-Like Stars; p 99-102
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  • 2
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    The Resonant Count Diagram and Solar g Mode Oscillations (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Evidence is provided to support the hypothesis that, because of the particular frequency separations of the solar g modes, resonant three-wave interactions stimulate only a selected few g modes. A resonant count diagram was obtained by plotting the total number of possible resonant three-wave interactions or a given beat frequency against the inverse of the beat frequency (the beat period), within a given frequency tolerance. The 1 = 1, 2, 3, 4 g modes calculated by Christensen-Dalsgaard, Gough and Morgan (1979) for a standard model of the Sun were used. The diagram has a significant peak at 160 minutes as well as other peaks at longer periods. The g modes that Delache and Scherrer (1983) tentatively identified from the Crimea-Stanford data were also plotted. These modes were found to correspond with the other peaks in the diagram. This coincidence between the observed g modes and the peaks in the resonant count diagram suggest that the observed g modes do owe their observability to resonant three-wave interactions.
    Keywords: SOLAR PHYSICS
    Type: JPL Solar Seismology from Space.; p 349-350
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  • 3
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    Stellar models with microscopic diffusion and rotational mixing. 1: Application to the Sun (1995)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The Yale stellar evolution code has been modified to include the combined effects of diffusion and rotational mixing on H-1, H-4, and the trace elements He, Li-6, Li-7, and Be-9. The interaction between rotational mixing and diffusion is studied by calculating a number of calibrated solar models. The rotational mixing inhibits the diffusion in the outer parts of the models, leading to a decrease in the envelope diffusion by 25%-50%. Conversely, diffusion leads to gradients in mean molecular weight which can inhibit the rotational mixing. The degree to which gradients in mean molecular weight inhibit the rotational mixing is somewhat uncertain. A comparison with the observed solar oblateness suggests that gradients in the mean molecular weight play a smaller role in inhibiting the rotational mixing than previously believed. This is reinforced by the fact that the model with the standard value for the inhibiting effect of mean molecular weight on the rotational mixing depletes no Li on the main sequence. This is clear in contrast to the observations. A reduction in the inhibiting effect of mean molecular weight gradients by a factor of 10 loads to noticeable main-sequence Li depletion.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 441; 2; p. 865-875
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  • 4
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    Evolutionary models of the rotating sun (1989)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: A new rotating stellar evolution code is developed and applied to the sun. A hydrostatic fully convective premain-sequence model is evolved to the age of the sun. As the model evolves, it accounts for angular-momentum loss via a magnetic wind and angular-momentum redistribution by rotationally induced instabilities. The resulting models have an oblateness in agreement with observed upper limits. The rotation curves show two main features: the outer layers exhibit minimal radial differential rotation, and a rapidly rotating central core is preserved. These basic features persist through a wide range of model parameters.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 338; 424-452
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  • 5
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    The effect of the Mihalas, Hummer, and Daeppen equation of state and the molecular opacity on the standard solar model (1991)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Improvements to the Yale Rotating Stellar Evolution Code (YREC) by incorporating the Mihalas-Hummer-Daeppen equation of state, an improved opacity interpolation routine, and the effects of molecular opacities, calculated at Los Alamos, have been made. the effect of each of the improvements on the standard solar model has been tested independently by computing the corresponding solar nonradial oscillation frequencies. According to these tests, the Mihalas-Hummer-Daeppen equation of state has very little effect on the model's low l p-mode oscillation spectrum compared to the model using the existing analytical equation of state implemented in YREC. On the other hand, the molecular opacity does improve the model's oscillation spectrum. The effect of molecular opacity on the computed solar oscillation frequencies is much larger than that of the Mihalas-Hummer-Daeppen equation of state. together, the two improvements to the physics reduce the discrepancy with observations by 10 microHz for the low l modes.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 378; 407-412
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  • 6
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    The Sun as a probe of varying G (1994)
    In:  Other Sources
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    Publication Date: 2019-08-27
    Description: 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.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 437; 2; p. 870-878
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  • 7
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    Standard solar model (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: A set of solar models have been constructed, each based on a single modification to the physics of a reference solar model. In addition, a model combining several of the improvements has been calculated to provide a best solar model. Improvements were made to the nuclear reaction rates, the equation of state, the opacities, and the treatment of the atmosphere. The impact on both the structure and the frequencies of the low-l p-modes of the model to these improvements are discussed. It is found that the combined solar model, which is based on the best physics available (and does not contain any ad hoc assumptions), reproduces the observed oscillation spectrum (for low-l) within the errors associated with the uncertainties in the model physics (primarily opacities).
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 387; 372-393
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  • 8
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    Standard solar model. II - g-modes (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: The paper presents the g-mode oscillation for a set of modern solar models. Each solar model is based on a single modification or improvement to the physics of a reference solar model. Improvements were made to the nuclear reaction rates, the equation of state, the opacities, and the treatment of the atmosphere. The error in the predicted g-mode periods associated with the uncertainties in the model physics is predicted and the specific sensitivities of the g-mode periods and their period spacings to the different model structures are described. In addition, these models are compared to a sample of published observations. A remarkably good agreement is found between the 'best' solar model and the observations of Hill and Gu (1990).
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 392; 1 Ju
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