ASTR 8000 STELLAR ATMOSPHERES AND SPECTROSCOPY

1. ASTR 8000STELLAR ATMOSPHERESAND SPECTROSCOPY Introduction & Syllabus Light and MatterSample Atmosphere

2. 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”

3. 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

4. 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

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 temperatureP pressure andn densitythat leads to spectra consistent with observations

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 …

10. 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(τ)

11. 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

12. 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

13. geometric depth optical depth density 682 km

14. 30000 10000 6000 4286 3333 Å

16. Comparison with Vega (A0 V): Flux

17. Comparison with Vega (A0 V): Lines