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Discordant Estimates of Mass-Loss Rates for O-Type Stars
Alex FullertonSTScI /HIA
Derck Massa (STScI/SGT) & Raman Prinja (UCL)
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
Mass-Loss Diagnostics
H emission: recombination 2
Thermal radio emission: free-free 2 UV resonance lines: scattering
Mass-Loss Diagnostics
H emission: recombination 2
Thermal radio emission: free-free 2 UV resonance lines: scattering
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
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
P V Morphology
Walborn et al., 2002 , ApJS, 141, 443
O6
O4
O2
O9.7
Wind Profile Fits to P V 1118, 1128
Fullerton, Massa, & Prinja 2006, ApJ, 637, 1025
O6
O8
O4 O5
O7.5
O9.5
A Mass Loss Discrepancy
Fullerton, Massa, & Prinja 2006, ApJ, 637, 1025
Empirical Ionization Fraction of P4+
Fullerton, Massa, & Prinja 2006, ApJ, 637, 1025
Similarly for the LMC
Massa, Fullerton, Sonneborn, & Hutchings 2003, ApJ, 586, 996
Critique
Assumptions Ways Out
• AP ~ Solar
• q(P4+)~1 somewhere• Standard Model
Critique
Assumptions Ways Out
• AP ~ Solar • AP ≤ 0.1 Solar
• q(P4+)~1 somewhere• Standard Model
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
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?]
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?]
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
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
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)
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.
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!
Back-Up Slides
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
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
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
Summary: Effects of Clumping
Sk -67°166 O4 If+
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))