Three-dimensional non-LTE modelling of solar carbon
PHYSICS · Multi-part · Fermi University Physics · Astrophysics & Cosmology · Stellar structure, energy generation and evolution · Stellar structure, energy generation and evolution
Stars from the Inside, Ch The Sun as a test: calibration, sound, neutrinos and a magnetised atmosphere
Problem
Three-dimensional non-LTE modelling of solar carbon, nitrogen and oxygen lines revised the spectroscopic ratio Z/X from about 0.023 to about 0.018, a fractional reduction of 22% in the derived heavy-element abundance. Standard solar models built with the revised, lower mixture push the predicted convection-zone base outward from about 0.712R⊙ to about 0.725R⊙, a shift of about 0.013R⊙; helioseismic inversions locate the base to ±0.003R⊙.
((a)) State briefly, citing each link, the physical chain by which a lower derived Z/X (read from an equivalent width on the linear part of the curve of growth, Wλ∝N) changes the model's predicted convection-zone base.
((b)) Suppose an independent re-analysis of the same lines found only a 10% reduction in the derived heavy-element abundance (rather than 22%), everything else unchanged. Assuming the shift in the convection-zone base scales in proportion to the fractional change in Z, estimate the shift Δrcz this smaller revision would produce, and express it as a multiple of the seismic uncertainty σ=0.003R⊙.