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ASTR 8000 STELLAR ATMOSPHERES AND SPECTROSCOPY Introduction & Syllabus Light and Matter Sample Atmosphere 1 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” 2 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 3 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 4 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 5 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 … 6 7 8 9 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 10 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 11 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 12 optical depth geometric depth density 13 682 km 30000 10000 6000 4286 3333 Å 14 15 Comparison with Vega (A0 V): Flux 16 Comparison with Vega (A0 V): Lines 17