Osmania University - M.Sc ASTRONOMY - 3 - Theory Paper 9: Stellar Atmospheres

Theory Paper 9: Stellar Atmospheres

Unit 1
Equation of transfer

Definitions concerning the radiation field. Equation of transfer. Hypothesis of plane parallel and spherically symmetric stratification. Formal solution for this case. Local thermodynamic equilibrium. Radiative equilibrium. Grey approximation. Departures from greyness. Blanketing effect.

Unit 2
Continuous spectrum of the stars

Limb darkening observations of the sun. Determination of absorption co-efficient from Limb darkening observations. Sources of continuous opacity in various types of stars. Discussion of convection zones in stellar atmospheres.

Unit 3
Formation of absorption lines

Description of the stellar spectra. Types of line profiles .Schuster-Schwarzschild model with pure scattering in the line. Milne-Eddington model with pure absorption and scattering. Central intensities of resonance lines. Effect of interlocking and non-coherent scattering. Variation of line profiles across the solar disc. Saha-Boltzmann equation of ionization. LTE and Non LTE-two level atom. Moving atmospheres. Extended layers of stars.

Unit 4
Production of emission lines

Mechanism of emission line formation: Thermal emission and its application. Flourescence. Rosseland cycle. Zanstra’s mechanism, Bowen’s mechanism, Collisional excitation.


1) L.H.Aller: Astrophysics.
2) Greenstein(Ed): Stellar Atmospheres.
3) Hynek: Astrophysics.
4) Mihalas: Stellar Atmospheres.
5) Ambartzumian: Theoretical Astrophysics
6) K.D.Abhyankar: Astrophysics Stars and Galaxies.
7) Contributions of Dominion Obs.1929 (Beal's article)

Reference: http://osmania.ac.in

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