discordant estimates of mass-loss rates for o-type stars

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))