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Proc. Neutrino Astrophysics - MPP Theory Group

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Garching Solar Model: Present Status<br />

H. Schlattl, A. Weiss<br />

Max-Planck-Institut für Astrophysik, Karl Schwarzschild-Str. 1, 85748 Garching, Germany<br />

The Garching solar model code is designed to calculate high precision solar models. It allows<br />

to control the numerical accuracy and has the best available input physics implemented [1].<br />

It uses the OPAL-equation of state [2] and for the opacities those of [3] complemented by [4]<br />

in the low-temperature regions. Pre-main sequence evolution is also taken into account. The<br />

microscopic diffusion of hydrogen, helium, the isotopes participating in the CNO-cycle and<br />

some additional metals (Ne, Mg, Si) is incorporated following the description of [5] for the<br />

diffusion constants. The nuclear reaction rates were taken from [6].<br />

In this work we want to emphasize the sensitivity of the structure of a solar model on the<br />

interpolation technique used for the opacity tables. As the run of opacities (κ) with temperature<br />

(T) and/or density (ρ) may show very rapidly changing gradients, choosing a suitable<br />

interpolation procedure is not trivial. Our program uses two-dimensional bi-rational cubic<br />

splines [7] to interpolate in the T-R-grid of the opacity tables (R = ρ/T 3 6 , T6 = T/10 6 K).<br />

Apart from the general problem to choose suitable outer boundary conditions for the calculation<br />

of the spline functions one can introduce an additional parameter to avoid artificial<br />

unphysical oscillations, as they are typical in the case of cubic splines and rapidly varying<br />

slopes. Increasing this damping parameter leads to almost linear interpolation just between<br />

two grid points and to a very rapidly changing gradient at the grid points themselves. The<br />

higher the damping parameter the more extended gets the linear region (a value of 0 corresponds<br />

to standard cubic splines). The disadvantage of this damping is that in regions where<br />

Figure 1: The run of κ and dlogκ/dlogR with R at fixed temperature of 2 million Kelvin<br />

using pure cubic splines (dashed line) and damped cubic splines (full line). The arrows mark<br />

the value of R at this temperature in a typical solar model.<br />

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