Updating standard solar models

Ciacio, F.; Degl’Innocenti, S.; Ricci, B.

doi:10.1051/aas:1997168

Cited by 57 publications

(55 citation statements)

References 15 publications

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“…By using FRANEC [14], a stellar evolutionary code including diffusion of helium and heavy elements [15], we constructed solar models based on four different assumptions: i) The weak screening approximation (WES). The screening factors f ij are given by:…”

Section: Results Of Solar Model Calculations For Different Screenmentioning

confidence: 99%

Helioseismology and screening of nuclear reactions in the Sun

2001

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Section: Results Of Solar Model Calculations For Different Screenmentioning

confidence: 99%

Helioseismology and screening of nuclear reactions in the Sun

2001

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“…This deepening is additional to that of the convection zone itself, in the early Sun relative to today's Sun, amounting to several more tens of megametres according to standard solar models (e.g. Ciacio et al 1997). The early Sun would have started to form its helium settling layer just below the ventilated, lithium-destroying polar regions, i.e.…”

Section: Discussionmentioning

confidence: 99%

Polar confinement of the Sun's interior magnetic field by laminar magnetostrophic flow

Wood

McIntyre

2011

J. Fluid Mech.

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The global-scale interior magnetic field Bi needed to account for the Sun's observed differential rotation can be effective only if confined below the convection zone in all latitudes including, most critically, the polar caps. Axisymmetric solutions are obtained to the nonlinear magnetohydrodynamic equations showing that such polar confinement can be brought about by a very weak downwelling flow U ~ 10−5cms−1 over each pole. Such downwelling is consistent with the helioseismic evidence. All three components of the magnetic field B decay exponentially with altitude across a thin, laminar ‘magnetic confinement layer’ located at the bottom of the tachocline and permeated by spiralling field lines. With realistic parameter values, the thickness of the confinement layer ~10−3 of the Sun's radius, the thickness scale being the magnetic advection–diffusion scale δ = η/U where the magnetic (ohmic) diffusivity η ≈ 4.1 × 102cm2s−1. Alongside baroclinic effects and stable thermal stratification, the solutions take into account the stable compositional stratification of the helium settling layer, if present as in today's Sun, and the small diffusivity of helium through hydrogen, χ ≈ 0.9 × 101cm2s−1. The small value of χ relative to η produces a double boundary-layer structure in which a ‘helium sublayer‘ of smaller vertical scale (χ/η)1/2δ is sandwiched between the top of the helium settling layer and the rest of the confinement layer. Solutions are obtained using both semi-analytical and purely numerical, finite-difference techniques. The confinement-layer flows are magnetostrophic to excellent approximation. More precisely, the principal force balances are between Lorentz, Coriolis, pressure-gradient and buoyancy forces, with relative accelerations negligible to excellent approximation. Viscous forces are also negligible, even in the helium sublayer where shears are greatest. This is despite the kinematic viscosity being somewhat greater than χ. We discuss how the confinement layers s at each pole might fit into a global dynamical picture of the solar tachocline. That picture, in turn, suggests a new insight into the early Sun and into the longstanding enigma of solar lithium depletion.

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“…Brunish et al 1990), we adopted the updated rates by Hammer et al (2005) for the 12 C+α and by the LUNA collaboration (see Imbriani et al 2005, and references therein) for the 14 N + p cross sections. For the other nuclear reactions we adopted the same rates as in Ciacio et al (1997). The code implements weak screening (Salpeter 1954), weak-intermediate, intermediate-strong screening (Graboske et al 1973), and strong screening (Itoh et al 1977(Itoh et al , 1979.…”

Section: Evolutionary Stellar Modelsmentioning

confidence: 99%

Uncertainties on the theoretical predictions for classical Cepheid pulsational quantities

Valle

Marconi²,

Degl’Innocenti

et al. 2009

A&A

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Context. With their period-luminosity relation, "classical Cepheids" (CC) are the most common primary distance indicators within the Local Group, also providing an absolute calibration of important secondary distance indicators. However, the predicted position of these pulsators in the HR diagram, along the so called blue loop, that is the expected distribution of Cepheids within the instability strip is affected by several model inputs, reflecting upon the predicted PL relation. Aims. The aim of this work is to quantitatively evaluate the effects on the theoretical PL relation of current uncertainties on the chemical abundances of Cepheids in the Large Magellanic Cloud (LMC) and on several physical assumptions adopted in the evolutionary models. We will separately analyse how the different factors influence the evolutionary and pulsational observables and the resulting PL relation. Methods. To achieve this goal we computed new sets of updated evolutionary and pulsational models. Results. As a result, we find that present uncertainties on the most relevant H and He burning reaction rates do not influence in a relevant way the loop extension in temperature. On the contrary, current uncertainties on the LMC chemical composition significantly affect the loop extension and also reflect in the morphology of the instability strip; however their influence on the predicted pulsational parameters is negligible. We also discussed how overshooting and mass loss, sometimes suggested as possible solutions for the long-standing problem of the Cepheid mass discrepancy, influence the ML relation and the pulsational parameters. Conclusions. In summary, the present uncertainties on the physical inputs adopted in the evolutionary codes and in the LMC chemical composition are negligible for the prediction of the main pulsational properties. On the other hand, the inclusion of overshooting in the previous hydrogen burning phase and/or of mass loss is expected to significantly change the resulting theoretical pulsational scenario for Cepheids, as well as the calibration of their distance scale. These systematic effects are expected to influence the theoretical Cepheid calibration of the secondary distance indicators and in turn the resulting evaluation of the Hubble constant.

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Updating standard solar models

Cited by 57 publications

References 15 publications

Helioseismology and screening of nuclear reactions in the Sun

Helioseismology and screening of nuclear reactions in the Sun

Polar confinement of the Sun's interior magnetic field by laminar magnetostrophic flow

Uncertainties on the theoretical predictions for classical Cepheid pulsational quantities

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