Transcript STELLAR ATMOSPHERES

ASTR 8000
STELLAR ATMOSPHERES
AND SPECTROSCOPY
Introduction & Syllabus
Light and Matter
Sample Atmosphere
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Introductions and Syllabus
• Available on-line at class web site
http://www.astro.gsu.edu/~gies/ASTR8000/
• Texts
Gray “Stellar Photospheres” (older editions OK)
Mihalas “Stellar Atmospheres” (out of print)
Mihalas2 “Radiation Hydro” ($21)
Collins “Fundamentals” available on-line at
http://ads.harvard.edu/books/1989fsa..book/
Bohm-Vitense “Stellar Astrophysics Vol. 2”
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Rutten (Utrecht) Notes On-line
• Radiative Transfer in Stellar Atmospheres
http://www.astro.uu.nl/~rutten/Astronomy_lecture.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 in One!
• Astr 8000 Stellar Atmospheres
basics, building model atmospheres,
resulting continuous spectra, use to
determine properties of stars
Gray Chapters 1 – 10
• Astr 8600 Stellar Spectroscopy
detailed 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 temperature
P pressure and
n density
that 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
Physical description
of gas with depth:
example, T = T(τ)
Radiation field as a function
of frequency and depth to
make sure energy flow is
conserved
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Parameters
• Teff = Effective temperature defined by
integrated luminosity and radius
• log g = logarithm (base 10) of the surface
gravitational acceleration
• Chemical abundance of the gas
• Turbulence of the gas
• Magnetism, surface features, extended
atmospheres, and other complications
All potentially derivable from spectra
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Key Example:
Robert Kurucz and ATLAS
• Kurucz, R. L. 1979, ApJS, 40, 1
(http://kurucz.harvard.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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optical
depth
geometric
depth
density
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682 km
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
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