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