line shapes in hot stars : hydrodynamics & wind mass-loss rates
DESCRIPTION
Line Shapes in Hot Stars : Hydrodynamics & Wind Mass-Loss Rates. David Cohen Swarthmore College. with Maurice Leutenegger , Stan Owocki , Rich Townsend, Emma Wollman (‘09), James MacArthur (‘11). Pup (O4 If). Capella (G5 III) – coronal source – for comparison. Pup. Ne X. - PowerPoint PPT PresentationTRANSCRIPT
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Line Shapes in Hot Stars: Hydrodynamics & Wind Mass-Loss Rates
David CohenSwarthmore College
with Maurice Leutenegger, Stan Owocki, Rich Townsend, Emma Wollman (‘09), James MacArthur (‘11)
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Pup (O4 If)
Capella (G5 III) – coronal source – for comparison
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Pup
Capella
Ne X Ne IX Fe XVII
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Pupmassive
Capellalow mass
broad, skewed,
blue shifted
unresolved
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rad-hydro wind simulations: line-driving instability
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shock onset at r ~ 1.5 RstarVshock ~ 300 km/s :
T ~ 106 K
hot plasma has low density
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99% of the wind mass is cold*, partially ionized…x-ray absorbing
*typically 20,000 – 30,000 K; maybe better described as “warm”
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photoelectric absorption:continuum opacity in the cold wind component
CNO processed
solar abundance
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observer on left
isovelocity contours
-0.8vinf
-0.6vinf
-0.2vinf +0.2vinf
+0.6vinf
+0.8vinf
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observer on left
isovelocity contours
-0.8vinf
-0.6vinf
-0.2vinf +0.2vinf
+0.6vinf
+0.8vinf
optical depth
contours
t = 0.3
t = 1
t = 3
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M
4Rv
opacity of the cold wind component wind mass-loss rate
wind terminal velocityradius of the star
M4r2v
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t=1,2,8
key parameters: Ro & t*
M
4Rv
j ~ 2 for r/R* > Ro,
= 0 otherwise
Rdz'
r'2 (1 R r ')
z
Ro=1.5
Ro=3
Ro=10
=1 contours
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We fit these x-ray line profile models to each line in the Chandra data
Fe XVIIFe XVII
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And find a best-fit t* and Ro…
Fe XVIIFe XVII t* = 2.0
Ro = 1.5
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…and place confidence limits on these fitted parameter values
68, 90, 95% confidence limits
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z Pup: three emission lines
Mg Lya: 8.42 Å Ne Lya: 12.13 Å O Lya: 18.97 Å
t* = 1 t* = 2 t* = 3
Recall:
M
4Rv
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atomic opacity of the windCNO processed
Solar
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Results from the 3 line fits shown previously
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Fits to 16 lines in the Chandra spectrum of z Pup
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Fits to 16 lines in the Chandra spectrum of z Pup
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Fits to 16 lines in the Chandra spectrum of z Pup
M
4Rv
t*(l) trend consistent with k(l)
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M
4Rv
t*(l) trend consistent with k(l)
M becomes the free parameter of the fit to the t*(l) trend
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Traditional mass-loss rate: 8.3 X 10-6 Msun/yr
Our best fit: 3.5 X 10-6 Msun/yr
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Fe XVIITraditional mass-loss rate: 8.3 X 10-6 Msun/yr
Our best fit: 3.5 X 10-6 Msun/yr
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Ori: O9.5 e Ori: B0
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z Ori (09.7 I): O Lya 18.97 Å
Ro = 1.6 R*
t* = 0.3
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t* quite low: is resonance scattering affecting this line? - Next talk, by M. Leutenegger
Ro = 1.6 R*
t* = 0.3
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e Ori (B0 Ia): Ne Lya 12.13 Å
Ro = 1.5 R*
t* = 0.6
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HD 93129Aab (O2.5): Mg XII Lya 8.42 Å
Ro = 1.8 R*
t* = 1.4
M-dot ~ 2 X 10-5 Msun/yr
Vinf ~ 3200 km/s
M-dot ~ 5 X 10-6 Msun/yr
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Multi-wavelength evidence for lower mass-loss rates is emerging
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z Pup mass-loss rate < 4.2 X 10-6 Msun/yr
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“Clumping” – or micro-clumping: affects density-squared diagnostics; independent of clump size, just depends on
clump density contrast (or filling factor, f )
visualization: R. Townsend
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The key parameter is the porosity length,
h = (L3/ℓ2) = ℓ/f
But porosity is associated with optically thick clumps, it acts to reduce the effective opacity of the wind; it does
depend on the size scale of the clumps
L
ℓ
f = ℓ3/L3
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h = ℓ/f
clump size
clump filling factor (<1)
The porosity length, h:
Porosity length increasing
Clump size increasing
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Porosity only affects line profiles if the porosity length (h) exceeds the stellar radius
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The clumping in 2-D simulations (density shown below) is on quite small scales
Dessart & Owocki 2003, A&A, 406, L1
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No expectation of porosity from simulations
Natural explanation of line profiles without invoking porosity
Finally, to have porosity, you need clumping in the first place, and once you have clumping…you have your factor ~3
reduction in the mass-loss rate
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No expectation of porosity from simulations
Natural explanation of line profiles without invoking porosity
Finally, to have porosity, you need clumping in the first place, and once you have clumping…you have your factor ~3
reduction in the mass-loss rate
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No expectation of porosity from simulations
Natural explanation of line profiles without invoking porosity
Finally, to have porosity, you need clumping in the first place, and once you have clumping…you have your factor ~3
reduction in the mass-loss rate (for z Pup, anyway)
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f = 0.1
f = 0.2
f = 0.05
f ~ 0.1 is indicated by H-alpha, UV, radio free-
free analysis
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f = 0.1
f = 0.2
f = 0.05
And lack of evidence for porosity…leads us to
suggest visualization in upper left is closest to
reality
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conclusions
Line widths consistent with embedded wind shocks
Skewed line shapes consistent with photoelectric absorption; magnitude and wavelength trend enable a mass-loss rate measurement
Consistent explanation for zeta Pup – M down by factor of 3, no need to invoke porosity
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conclusions
Line widths consistent with embedded wind shocks
Skewed line shapes consistent with photoelectric absorption; magnitude and wavelength trend enable a mass-loss rate measurement
Consistent explanation for zeta Pup – M down by factor of 3, no need to invoke porosity
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conclusions
Line widths consistent with embedded wind shocks
Skewed line shapes consistent with photoelectric absorption; magnitude and wavelength trend enable a mass-loss rate measurement
Consistent explanation for zeta Pup – M down by factor of 3, no need to invoke porosity
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conclusions
Line widths consistent with embedded wind shocks
Skewed line shapes consistent with photoelectric absorption; magnitude and wavelength trend enable a mass-loss rate measurement
Consistent explanation for zeta Pup – M down by factor of 3, no need to invoke porosity