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Exploring Stellar Atmospheres and Spectroscopy: A Comprehensive Guide

This course delves into the basics of stellar atmospheres, models, continuous spectra, and their use in determining star properties. It also covers detailed spectroscopic analysis of stars, line spectra, methods, and practical applications. The syllabus, textbooks, grading system, presentations, and key examples are outlined for a clear understanding. Topics include radiation fields, physical gas descriptions, parameters like effective temperature and surface gravity, and the example of Robert Kurucz's ATLAS models. Special focus is given to phenomena beyond standard models, like rotation, convection, magnetism, and spots. The instrumental CHARA Array and notable observations in stellar atmospheres are highlighted.

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Exploring Stellar Atmospheres and Spectroscopy: A Comprehensive Guide

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

  2. A brief bio • 1968-74 RASC member • 1974-84 University of Toronto, DDO • 1984-88 McDonald Obs., Univ. Texas • 1988-present GSU Physics & Astronomy • 2015-present CHARA Director • Introductions

  3. Two 3CH Courses into One 4CH! • Astr 8000 Stellar Atmospheresbasics, building model atmospheres, resulting continuous spectra, use to determine properties of stars • Astr 8600 Stellar Spectroscopydetailed look at the line spectra of stars (bound-bound transitions), methods, applications

  4. Introductions and Syllabus • Available on-line at class web sitehttp://www.astro.gsu.edu/~gies/ASTR8000/

  5. Text Books • Ivan Hubeny & Dimitri Mihalas “Theory of Stellar Atmospheres” • Richard Gray & Chris Corbally“Stellar Spectral Classification”Main source for class presentations • David Gray “The Observation and Analysis of Stellar Photospheres” • George Collins “Fundamentals of Stellar Ap.”http://ads.harvard.edu/books/1989fsa..book/

  6. Robert Rutten (Utrecht) Notes On-line • Radiative Transfer in Stellar Atmosphereshttp://www.staff.science.uu.nl/~rutte101/Radiative_Transfer.html • Good set of notes that emphasizes the physical aspects of atmospheres & Sun • We will use these notes frequently

  7. Grades • Grades based uponclass presentation 20%4 problem sets 40%midterm exam 20%final exam 20% • Class 10:00-10:50, 11:00-11:50 am • Midterm as take home • Exam in class: May 2, 10 am - noon

  8. Presentations from Gray & Corbally book • Jan 24 O StarsRobinson • Jan 31 B StarsCouperus • Feb 7 A StarsGulledge • Feb 14 F StarsMerritt • Feb 21 G & K StarsJames • Mar 7 M giantsShepard • Mar 14 M & L dwarfsHall • Mar 28 T & Y dwarfsNisak • Apr 4 WR, LBVMedan • Apr 11 EndpointsReyes

  9. 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

  10. 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 …

  11. 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)

  12. 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

  13. Key Example: Robert Kurucz and ATLAS • Kurucz, R. L. 1979, ApJS, 40, 1(http://kurucz.harvard.edu/) • Plane parallel, LTE, line-blanketed modelsLTE = local thermodynamic equilibriumexcitation, ioniziation states set by T • Current version ATLAS12 runs in Linux • Units: c.g.s. and logarithms for most • Example: Sun

  14. geometric depth optical depth density 682 km

  15. 30000 10000 6000 4286 3333 Å

  16. Comparison with Vega (A0 V): Flux

  17. Comparison with Vega (A0 V): Lines

  18. Beyond Plane-Parallel Model • Rotation • Extended atmospheres • Granulation • Magnetism • Spots …Long baselineinterferometry:CHARA Array

  19. Rotation

  20. Wind of P Cygni Richardson et al.2013, ApJ, 769, 118

  21. Convection: Red Supergiants CHARA/MIRC H-band of AZ Cyg (Ryan Norris & Fabien Baron) 3D simulation by Chiavassa et al. (2011)

  22. Magnetically active star Persistent polar spot Transient lower latitude spots Starspots Zeta Andromedae θ = 2.5 mas Roettenbacher et al. 2016, Nature, 533, 217

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