1. 1 ASTR 8000 STELLAR ATMOSPHERES AND SPECTROSCOPY Introduction & Syllabus Light and Matter Sample Atmosphere

2. 2 Introductions and Syllabus Available on-line at class web site http://www.astro.gsu.edu/~gies/ASTR8000/ http://www.astro.gsu.edu/~gies/ASTR8000/ Texts Gray “Stellar Photospheres” (older editions OK) Mihalas “Stellar Atmospheres” (out of print) Mihalas 2 “Radiation Hydro” ($21) Collins “Fundamentals” available on-line at http://ads.harvard.edu/books/1989fsa..book/ Bohm-Vitense “Stellar Astrophysics Vol. 2”

3. 3 Rutten (Utrecht) Notes On-line Radiative Transfer in Stellar Atmospheres http://www.astro.uu.nl/~rutten/Astronomy_lecture.html 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

4. 4 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

5. 5 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

6. 6 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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10. 10 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

11. 11 Parameters T eff = 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

12. 12 Key Example: Robert Kurucz and ATLAS Kurucz, R. L. 1979, ApJS, 40, 1 (http://kurucz.harvard.edu/)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

13. 13 682 km geometric depth density optical depth

14. 14 30000 10000 6000 4286 3333 Å

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16. 16 Comparison with Vega (A0 V): Flux

17. 17 Comparison with Vega (A0 V): Lines