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Stellar Physics: Stellar Atmospheres (13) Stellar Structure & Interiors (11)

Stellar Physics: Stellar Atmospheres (13) Stellar Structure & Interiors (11). Kenneth Wood, Room 316 kw25@st-andrews.ac.uk http://www-star.st-and.ac.uk/~kw25. Course Texts. Radiative Transfer in Stellar Atmospheres (Rutten) On web and in library Stellar Structure & Evolution (Prialnik)

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Stellar Physics: Stellar Atmospheres (13) Stellar Structure & Interiors (11)

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  1. Stellar Physics:Stellar Atmospheres (13)Stellar Structure & Interiors (11) Kenneth Wood, Room 316 kw25@st-andrews.ac.uk http://www-star.st-and.ac.uk/~kw25

  2. Course Texts • Radiative Transfer in Stellar Atmospheres (Rutten) On web and in library • Stellar Structure & Evolution (Prialnik) • Stellar Atmospheres (Mihalas) • Observation & Analysis of Stellar Photospheres (Gray)

  3. Lectures, Tutorials, & Exam • 27 scheduled lectures • Coursework: 24 lectures (including today) • 2 Tutorial sheets. Do you want more? • Lecture notes on web • Degree Exam in January • 3 long questions: answer 2 • 5 short questions: answer all

  4. What is a Stellar Atmosphere? • Transition from dense stellar interior to interstellar medium. • Region that produces the stellar spectrum. The physical depths in the atmosphere where the spectral features form depend on the atmospheric conditions: temperature, density, level populations, optical depth… • We see radiation from the “optical depth one surface” • Goal: From analysis of spectral lines and continua, determine physical conditions, chemical abundances, mass loss rates…

  5. Balmer Lines & Balmer Jump a Lyra • H-opacity ~ l3 • Jump at Balmer “series limit” • Size of jump: estimate temperature & pressure

  6. Model Atmosphere • Expect “saw tooth” due to H opacity • Line blanketing…

  7. Line Blanketing • UV opacity from metals • Blocks flux: blanketing • Fe, Al,… • Temperature diagnostic

  8. P-Cygni Line Profiles • Expanding atmosphere or stellar wind • Wind speed from blue edge • UV space astronomy (1960s): wind theories

  9. Simplifications, but not simple… • Plane parallel • Time independent • Hydrostatic equilibrium • No magnetic fields

  10. The Sun

  11. The Solar Corona

  12. What happens physically? • Photons emitted, travel some distance, interact with atmospheric material • Scattered, absorbed, re-emitted • Photon interactions heat atmosphere, change level populations, ionization balance • Hydrostatic equilibrium: density structure related to temperature structure • Atmospheric structure depends on radiation field and vice versa • Atmosphere model requires detailed study of radiation transfer: bulk of this course

  13. Stellar Atmospheres & Radiation Transfer: 13 Lectures • Radiation transfer recap: equations, definitions (2) • Opacity sources & LTE (2) • Formal, approximate & analytic solutions (3) • Model atmospheres (1) • Spectral lines (2) • Circumstellar material: Monte Carlo (3)

  14. 2. Radiation Field Basics I • Rutten: 2.1 • Basic definitions of intensity, flux • Energy density, radiation pressure

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