Absorption Cross Sections (Mihalas Chapter 4)

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Absorption Cross Sections (Mihalas Chapter 4). Bound-bound transitions (Einstein relations) Bound-free transitions (Einstein-Milne relations). Bound-Bound Transitions. Balance transitions between two levels Upwards absorption Downwards by spontaneous or stimulated emission. j. h ν ij. i.

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### Absorption Cross Sections(Mihalas Chapter 4)

Bound-bound transitions(Einstein relations)Bound-free transitions(Einstein-Milne relations)

Bound-Bound Transitions
• Balance transitions between two levels
• Upwards absorption
• Downwards by spontaneous or stimulated emission

j

hνij

i

Return Rates: Aji=Einstein coeff. spontaneous em.Bji=Einstein coeff. stimulated em.

(isotropic)

(same direction as Iν)

Transition Rates
• Calculate or measure cross section
Transition Rates: Hydrogen
• H transitions n\'→n
Einstein-Milne Relations:energy and velocity

Replace v dv increment in recombination term with this.

b-f Transfer Equation

T.E.: αν=pνhν , ne=Maxwellian, n0*/n1*=Saha, G(v)/pν above …