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Diagnostics of Inhomogeneity in the Outer Atmospheres/Winds of M Supergiants

Diagnostics of Inhomogeneity in the Outer Atmospheres/Winds of M Supergiants. Alexander Brown Center for Astrophysics and Space Astronomy University of Colorado at Boulder. Collaborators. Graham Harper (CASA/Colorado) – PI of projects Matt Richter (UC Davis -TEXES)

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Diagnostics of Inhomogeneity in the Outer Atmospheres/Winds of M Supergiants

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  1. Diagnostics of Inhomogeneity in the Outer Atmospheres/Winds of M Supergiants Alexander Brown Center for Astrophysics and Space Astronomy University of Colorado at Boulder

  2. Collaborators • Graham Harper (CASA/Colorado) – PI of projects • Matt Richter (UC Davis -TEXES) • Joanna Brown (Caltech  MPE) • Shadrian Strong (UT Austin), Tommy Greathouse (LPI), Andrew Kruger (UC) Cool Stars XV - Supergiant Splinter Session

  3. Overview • How we observe M supergiants determines what we see • Temperature Inhomogeneity --- UV spectrum: the Hot View; Radio Continuum : the Cold View • Density/Pressure Inhomogeneity --- Spatially resolved CII] electron densities and flow velocities – HST/STIS • Kinematic/Turbulence Inhomogeneity --- Mid-Infrared [Fe II] 17.9 & 24.5 μm Diagnostics – TEXES (IRTF/Gemini N) Cool Stars XV - Supergiant Splinter Session

  4. Betelgeuse – Hot Alfvén Model UV spectra show many emission lines (Mg II, Fe II, C II) typically formed at chromospheric temperatures. FOC UV Diameter 2x optical photosphere: Gilliland & Dupree 1996, ApJ, 463, L29 Linear Alfvén wave-driven winds: Hartmann & Avrett 1984, ApJ, 284, 238 Cool Stars XV - Supergiant Splinter Session

  5. Very Large Array: 7mm spatially-resolved image First resolved radio results: Lim et al. 1998 Nature, 392, 575 VLA image courtesy of NRAO/AUI and Laure Nelson Neish Cool Stars XV - Supergiant Splinter Session

  6. Betelgeuse: Cool “radio” models UV: Gilliland & Dupere HST/FOC Multi-frequency VLA+PT imaging Green=new cool model atmosphere Cool Stars XV - Supergiant Splinter Session

  7. Spatially Sampling the Hot Plasma Stepped STIS E230M 100x25 mas Slit [-75->+75mas] (over VLA K band image) C II] 2325 A Multiplet (+50 mas offset) Cool Stars XV - Supergiant Splinter Session

  8. Electron Density Diagnostics Cool Stars XV - Supergiant Splinter Session

  9. Electron density – as function of offset Open symbols --- individual STIS NW-SE scans Filled blue dots --- W–E scan Cool Stars XV - Supergiant Splinter Session

  10. Observation (right) versus model (left) Cool Stars XV - Supergiant Splinter Session

  11. Hiding the Hot Stuff κλ=nenion f(Te)2.1 Hot plasma 102-4 more opaque Radio seeks out hot plasma - but we observe cool plasma - hot plasma has tiny filling-factor What geometry of structures can do this? Shells, radial tubes? Cool Stars XV - Supergiant Splinter Session

  12. Results from the “Hot” Component • Chromospheric electron density • 107-9 cm-3 1-2 orders of magnitude higher than cool gas • changes by an order of magnitude over ΔR=R* • C II] emission lines • opacity broadened at limb • turbulence quite isotropic and uniform • Emission at rest with C-o-M of star (i.e. typical). • Chromosphere is pervasive on large spatial scales • rotationally decouples very rapidly Harper & Brown (2006) ApJ, 646, 1179 Cool Stars XV - Supergiant Splinter Session

  13. Infrared forbidden Fe II Cool Stars XV - Supergiant Splinter Session

  14. TEXES & IRTF/Gemini-N • TEXas Echelon-cross-Echelle Spectrograph: sister of EXES • PI John Lacy (hiding below) • Matt Richter (UC Davis) Cool Stars XV - Supergiant Splinter Session

  15. TEXES Characteristics • The following is an unpaid advertisement - • R=50,000 at 25 μm (evacuated water cell) • Wavelength scale: good to better 1 kms-1 • Radiometric flux corrections • Telluric water features removed to 10% level • 3m IRTF 2 arcsec FWHM= jitter-ball+seeing+diffraction • Nod 6 arcsec with 2 arcsec dispersion slit • 8m Gemini-N improved diffraction+pointing • Less efficient than nods, less optimized for mid-IR • To be explored • Real time IDL data collection/visualization software Cool Stars XV - Supergiant Splinter Session

  16. Betelgeuse – [Fe II], [Fe I] Cool Stars XV - Supergiant Splinter Session

  17. M Supergiants Line/continuum contrast: -silicate dust emission -mass-loss rate -wind temperature Cool Stars XV - Supergiant Splinter Session

  18. M Supergiants II Line width: single stars Vturb=11 kms-1 α Sco (M1.5 Iab + B3 V) IRTF & Gemini-N profiles similar - triangular shape Cool Stars XV - Supergiant Splinter Session

  19. The Full Extent Cool Stars XV - Supergiant Splinter Session

  20. Summary of [Fe II] Results • Excitation temperature of TEXES/ISO lines • ISO = Te=1250 K & TEXES > 2000 K • Formed close to star • Line formation coupled to continuum • part chromospheric/part wind • Dynamically different from ”hot” component • Vturb=10-12 kms-1 (cool) vs. 17-19 kms-1(hot) • Vcent~ 0 kms-1 (wind flow still not seen!) • All M supergiants observed show [Fe II] • Properties not unique to Betelgeuse Harper et al. (2008, in prep). Cool Stars XV - Supergiant Splinter Session

  21. The End Thank You. But ……….. see Poster M5 --- Graham’s CO investigations Cool Stars XV - Supergiant Splinter Session

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