A magnesium (Mg I) absorption line at forms in a stellar photosphere at

PHYSICS · Multi-part · Fermi University Physics · Astrophysics & Cosmology · Radiation, radiative transfer and stellar atmospheres · Radiation, radiative transfer and stellar atmospheres

Stars from the Inside, Ch Radiative transfer solved: the grey atmosphere, the diffusion limit and the curve of growth

Problem

A magnesium (Mg I) absorption line at λ=517 nm\lambda = 517\,\mathrm{nm} forms in a stellar photosphere at T=8000 KT = 8000\,\mathrm{K}. The magnesium atomic mass is 24.305 u24.305\,u and the upper level's total decay rate is Γ=5.0×107 s−1\Gamma = 5.0\times10^{7}\,\mathrm{s^{-1}}. Ignore microturbulence and pressure broadening. ((a)) Find the Doppler width ΔλD\Delta\lambda_D. ((b)) Find the natural width ΔλN=λ2Γ/2πc\Delta\lambda_N = \lambda^2\Gamma/2\pi c. ((c)) State how many times narrower the natural width is than the Doppler width.

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