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ASTR 8000STELLAR ATMOSPHERES

AND SPECTROSCOPYIntroduction & Syllabus

Light and MatterSample Atmosphere

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Introductions and Syllabus

• Available on-line at class web sitehttp://www.astro.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/Bohm-Vitense “Stellar Astrophysics Vol. 2”

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Rutten (Utrecht) Notes On-line

• Radiative Transfer in Stellar Atmosphereshttp://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 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

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 complicationsAll 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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682 km

geometric depth densityoptical

depth

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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