ASTR 8000 STELLAR ATMOSPHERES AND SPECTROSCOPY

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

11. 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

12. 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 …

16. 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)

17. 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

18. 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

19. geometric depth optical depth density 682 km

20. 30000 10000 6000 4286 3333 Å

22. Comparison with Vega (A0 V): Flux

23. Comparison with Vega (A0 V): Lines

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

25. Rotation

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

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

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