discordant estimates of mass-loss rates for o-type stars
DESCRIPTION
Discordant Estimates of Mass-Loss Rates for O-Type Stars. Alex Fullerton STScI /HIA Derck Massa (STScI/SGT) & Raman Prinja (UCL). Mass-Loss Diagnostics. H emission: recombination 2 Thermal radio emission: free-free 2 - PowerPoint PPT PresentationTRANSCRIPT
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Discordant Estimates of Mass-Loss Rates for O-Type Stars
Alex FullertonSTScI /HIA
Derck Massa (STScI/SGT) & Raman Prinja (UCL)
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Mass-Loss Diagnostics
H emission: recombination 2
Thermal radio emission: free-free 2 UV resonance lines: scattering
Kudritzki & Puls 2000, ARAA, 38, 613
O5 If+10.0 × 10-6 Msun/yr 7.5 5.0
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Mass-Loss Diagnostics
H emission: recombination 2
Thermal radio emission: free-free 2 UV resonance lines: scattering
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Mass-Loss Diagnostics
H emission: recombination 2
Thermal radio emission: free-free 2 UV resonance lines: scattering
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Mass-Loss Diagnostics
Thermal radio emission: free-free 2 H emission: recombination 2
UV resonance lines: scattering
Constants,Parameters
VelocityLaw
OpticalDepth
Ionization Fraction: 0 qi 1 Usually Don’t Know Usually Can’t Estimate
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UV Resonance Lines in Hot-Star Winds
P V λλ 1117.977, 1128.008
fblue, fred = 0.473, 0.234
Δv = 2690 km/s
(P/H)solar = 2.8 × 10-7
(P/C)solar = 8.5 × 10-4
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P V Morphology
Walborn et al., 2002 , ApJS, 141, 443
O6
O4
O2
O9.7
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Wind Profile Fits to P V 1118, 1128
Fullerton, Massa, & Prinja 2006, ApJ, 637, 1025
O6
O8
O4 O5
O7.5
O9.5
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A Mass Loss Discrepancy
Fullerton, Massa, & Prinja 2006, ApJ, 637, 1025
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Empirical Ionization Fraction of P4+
Fullerton, Massa, & Prinja 2006, ApJ, 637, 1025
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Similarly for the LMC
Massa, Fullerton, Sonneborn, & Hutchings 2003, ApJ, 586, 996
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Critique
Assumptions Ways Out
• AP ~ Solar
• q(P4+)~1 somewhere• Standard Model
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Critique
Assumptions Ways Out
• AP ~ Solar • AP ≤ 0.1 Solar
• q(P4+)~1 somewhere• Standard Model
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Critique
Assumptions Ways Out
• AP ~ Solar • AP ≤ 0.1 Solar
• q(P4+)~1 somewhere
• q(P4+) << 1 always
• Standard Model
Sutherland & Dopita 1993, ApJS, 88, 253
Puls et al. 2008, ASPC, 388, 101
Collisional Equilibria
v / v∞
v / v∞
O8 I O7 I
O6 I O5 I
q
q
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Critique
Assumptions Ways Out• AP ~ Solar • AP ≤ 0.1 Solar
• q(P4+)~1 somewhere
• q(P4+) << 1 always
• Standard Model • Relax Assumptions
–Spherically Symmetric–Stationary–Homogeneous–Monotonically expanding–Sobolev Approx. valid
–Aspherical (rotation?)–Time-Dependent–Inhomogeneous–Non-monotonic v(r)–[Sobolev valid?]
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Critique
Assumptions Ways Out• AP ~ Solar • AP ≤ 0.1 Solar
• q(P4+)~1 somewhere
• q(P4+) << 1 always
• Standard Model • Relax Assumptions
–Spherically Symmetric–Stationary–Homogeneous–Monotonically expanding–Sobolev Approx. valid
–Aspherical (rotation?)–Time-Dependent–Inhomogeneous–Non-monotonic v(r)–[Sobolev valid?]
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Consequences of Clumping (1)“Direct”:
Mass-loss rates determined from
ρ2 diagnostics are over-estimated.
“Indirect”:
The ionization stratification of the
wind is altered by enhancedrecombination in the clumps.
If all the P V - ρ2 discrepancy is assigned to the
ρ2 diagnostics, then
• The ρ2 mass-loss rates must be reduced by factor of at least 10; and
• Volume filling factors of << 0.01 are implied.
CMFGEN Model of HD 190429A (O4 If+)
Bouret, Lanz, & Hillier 2005, A&A, 438, 301
q(P4+) smooth wind
q(P4+) clumped wind
f∞ = 0.04
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Consequences of Clumping (2)Spatial Porosity:When clumps become optically thick, the effective opacity of the wind decreases because star light can find an unattenuated channelthrough the wind. Material can be hidden in the clumps.
“Macroclumping”:Not all transitions have the
sameoptical depth, so porosity
affectssome lines more than others.
“Velocity Porosity”:For line transfer, gaps in the
velocityprofile (“vorosity”) permit star light
toleak through the wind, irrespective
ofthe spatial porosity. This effectalso weakens an absorption
trough.
Oskinova, Hamann, & Feldmeier 2007, A&A, 476, 1331
ζ Puppis
O4 I(n)f
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Consequences of Clumping (2)Spatial Porosity:When clumps become optically thick, the effective opacity of the wind decreases because star light can find an unattenuated channelthrough the wind. Material can be hidden in the clumps.
“Macroclumping”:Not all transitions have the
sameoptical depth, so porosity
affectssome lines more than others.
“Velocity Porosity”:For line transfer, gaps in the
velocityprofile (“vorosity”) permit star light
toleak through the wind, irrespective
ofthe spatial porosity. This effectalso weakens an absorption
trough.
Owocki 2007 “Clumping in Hot-Star Winds” (Potsdam)
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Summary1) The discrepancy between mass-loss rates estimated
from P V and 2 diagnostics is very important. – The paradigm is evolving: winds are significantly structured.– But on what scale[s]? By what process[es]?
2) Consequently: – Mass-loss rates derived from 2 diagnostics are biased: too large.– Mass-loss estimates from P V are biased if the “clumps” are
optically thick: too small(?)– We don’t know what the mass-loss rates are to within ???– Concordance will likely require inclusion of several effects.– We need to use all available diagnostics to break multiple
degeneracies.
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Good Science Opens Doors“…the reasonable assumption that the mass loss rate for any star should be the same irrespective of which line is used …”
Conti & Garmany (1980, ApJ, 238, 190)
Questions!
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Back-Up Slides
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Why Was Clumping Ignored?
1. Absence of variability on flow time scale.
2. Mass fluxes determined at different radio wavelengths (i.e., radial distances) agreed.
3. The mass fluxes obtained from H (formed near the star) and the radio free-free continuum (formed far from the star) agree. Since it is unlikely that the clumping factor would be the same at both radii, it must be unity; i.e., no clumping.
Lamers & Leitherer (1993, ApJ, 412, 771):
Eversberg, Lépine, & Moffat 1998, ApJ, 494, 799Lépine & Moffat 2008, AJ, 136, 548
ζ Puppis O4 I(n)f
He II 4686
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Why Was Clumping Ignored?
1. Absence of variability on flow time scale.
2. Mass fluxes determined at different radio wavelengths (i.e., radial distances) agreed.
3. The mass fluxes obtained from H (formed near the star) and the radio free-free continuum (formed far from the star) agree. Since it is unlikely that the clumping factor would be the same at both radii, it must be unity; i.e., no clumping.
Lamers & Leitherer (1993, ApJ, 412, 771):
Blomme et al. 2003, A&A, 408, 715
ζ Puppis O4 I(n)f
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Why Was Clumping Ignored?
1. Absence of variability on flow time scale.
2. Mass fluxes determined at different radio wavelengths (i.e., radial distances) agreed.
3. The mass fluxes obtained from H (formed near the star) and the radio free-free continuum (formed far from the star) agree. Since it is unlikely that the clumping factor would be the same at both radii, it must be unity; i.e., no clumping.
Lamers & Leitherer (1993, ApJ, 412, 771):
Puls et al. 2006, A&A, 454, 625
ζ Puppis O4 I(n)f
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Summary: Effects of Clumping
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Sk -67°166 O4 If+
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Wind Profile Fits to P V 1118, 1128
Fullerton, Massa, & Prinja 2006, ApJ, 637, 1025
O7.5 III
O7 Ib(f) O7 II(f)
O7 V ((f))