Diagnostics of Inhomogeneity in the Outer Atmospheres/Winds of M Supergiants
description
Transcript of Diagnostics of Inhomogeneity in the Outer Atmospheres/Winds of M Supergiants
Diagnostics of Inhomogeneity in the Outer Atmospheres/Winds of M Supergiants
Alexander BrownCenter for Astrophysics and Space Astronomy
University of Colorado at Boulder
Tuesday, 22 July 2008Cool Stars XV - Supergiant Splinter Session 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)
Tuesday, 22 July 2008Cool 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)
Tuesday, 22 July 2008Cool Stars XV - Supergiant Splinter Session 4
Betelgeuse – Hot Alfvén Model
FOC UV Diameter 2x optical photosphere: Gilliland & Dupree 1996, ApJ, 463, L29
Linear Alfvén wave-driven winds: Hartmann & Avrett 1984, ApJ, 284, 238
UV spectra show many emission lines (Mg II, Fe II, C II) typically formed at chromospheric temperatures.
Tuesday, 22 July 2008Cool 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
Tuesday, 22 July 2008Cool 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
Tuesday, 22 July 2008Cool 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)
Tuesday, 22 July 2008Cool Stars XV - Supergiant Splinter Session 8
Electron Density Diagnostics
Tuesday, 22 July 2008Cool 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
Tuesday, 22 July 2008Cool Stars XV - Supergiant Splinter Session 10
Observation (right) versus model (left)
Tuesday, 22 July 2008Cool 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?
Tuesday, 22 July 2008Cool 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
Tuesday, 22 July 2008Cool Stars XV - Supergiant Splinter Session 13
Infrared forbidden Fe II
Tuesday, 22 July 2008Cool 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)
Tuesday, 22 July 2008Cool 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
Tuesday, 22 July 2008Cool Stars XV - Supergiant Splinter Session 16
Betelgeuse – [Fe II], [Fe I]
Tuesday, 22 July 2008Cool Stars XV - Supergiant Splinter Session 17
M Supergiants
Line/continuum contrast:
-silicate dust emission
-mass-loss rate
-wind temperature
Tuesday, 22 July 2008Cool 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
Tuesday, 22 July 2008Cool Stars XV - Supergiant Splinter Session 19
The Full Extent
Tuesday, 22 July 2008Cool 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).
Tuesday, 22 July 2008Cool Stars XV - Supergiant Splinter Session 21
The End
Thank You.
But ………..
see Poster M5 --- Graham’s CO investigations