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ASTR 8000 STELLAR ATMOSPHERES AND SPECTROSCOPY

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ASTR 8000STELLAR ATMOSPHERESAND SPECTROSCOPY

Introduction & Syllabus Light and MatterSample Atmosphere

- 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”

- 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

- 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

- 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

- 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 …

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)

- 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

- 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

geometric depth

optical depth

density

682 km

30000 10000 6000 4286 3333 Å