STELLAR ATMOSPHERES

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STELLAR ATMOSPHERES

• Introduction Syllabus Light and MatterSample
  Atmosphere

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Introductions and Syllabus

• Available on-line at class web sitehttp//www.cha
  ra.gsu.edu/gies/ASTR8000/
• TextsGray Stellar Photospheres (older editions
  OK)Mihalas Stellar Atmospheres (out of
  print)Mihalas2 Radiation Hydro (21)Collins
  Fundamentals available on-line
  athttp//ads.harvard.edu/books/1989fsa..book/Boh
  m-Vitense Stellar Astrophysics Vol. 2

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Rutten (Utrecht) Notes On-line

• Radiative Transfer in Stellar Atmosphereshttp//w
  ww.astro.uu.nl/rutten/Lecture_notes.html
• Good set of notes that emphasizes the physical
  aspects (versus the observational emphasis in
  Gray)
• We will use these notes frequently

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Two Courses

• Astr 8000 Stellar Atmospheresbasics, building
  model atmospheres, resulting continuous spectra,
  use to determine properties of starsGray
  Chapters 1 10
• Astr 8600 Stellar Spectroscopydetailed look at
  the line spectra of stars (bound-bound
  transitions), applications Gray Chapters 11 18

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Introduction

• Understand stars from spectra formed in outer
  1000 km of radius
• Use laws of physics to develop a layer by layer
  description of T temperatureP pressure andn
  densitythat leads to spectra consistent with
  observations

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First Approximation

• Stellar spectra are similar to a Planck black
  body function characterized by T
• Actually assign an effective temperature to stars
  such that the integrated energy flux from the
  star that from a Planck curve
• How good is this approximation? Depends on the
  type of star

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Two Parts to the Problem
Radiation field as a function of frequency and
depth to make sure energy flow is conserved
Physical description of gas with depth example,
T T(t)
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Parameters

• Teff Effective temperature defined by
  integrated luminosity and radius (K)
• log g logarithm (base 10) of the surface
  gravitational acceleration (c.g.s.)
• Chemical abundance of the gas
• Turbulence of the gas
• Magnetism, surface features, extended
  atmospheres, and other complicationsAll
  potentially derivable from spectra

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Key Example Robert Kurucz and ATLAS

• Kurucz, R. L. 1979, ApJS, 40, 1(http//kurucz.har
  vard.edu/)
• Plane parallel, LTE, line-blanketed models
• Current version ATLAS12 runs in Linux
• Units c.g.s. and logarithms for most
• Example Sun

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geometric depth
optical depth
density
682 km
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30000 10000 6000 4286
3333 Å
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Comparison with Vega (A0 V) Flux
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Comparison with Vega (A0 V) Lines