david cohen swarthmore college
DESCRIPTION
X-ray Spectroscopy of the Radiation-Driven Winds of Massive Stars: Line Profile and Line Ratio Diagnostics. David Cohen Swarthmore College. massive stars:. 20 to 100 M sun 10 6 L sun T ~ 50,000 K. Carina/Keyhole Nebula (HST). Chandra X-ray Telescope image of the Orion Nebula Cluster. - PowerPoint PPT PresentationTRANSCRIPT
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X-ray Spectroscopy of the X-ray Spectroscopy of the Radiation-Driven Winds of Massive Stars:Radiation-Driven Winds of Massive Stars:
Line Profile and Line Ratio DiagnosticsLine Profile and Line Ratio Diagnostics
David CohenDavid CohenSwarthmore CollegeSwarthmore College
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Carina/Keyhole Nebula (HST)Carina/Keyhole Nebula (HST)
massive stars: massive stars:
20 to 100 M20 to 100 Msunsun
101066 L Lsunsun
T ~ 50,000 KT ~ 50,000 K
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young, massive star: young, massive star: 11 Ori C Ori C
Chandra X-ray Telescope image of the Orion Nebula ClusterChandra X-ray Telescope image of the Orion Nebula Cluster
Color coded according to photon Color coded according to photon energy (red: <1keV; green 1 to 2 energy (red: <1keV; green 1 to 2 keV; blue > 2 keV)keV; blue > 2 keV)
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Whirlpool/M51 (HST)Whirlpool/M51 (HST)
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Crab Nebula (WIYN)Crab Nebula (WIYN)
1000 yr old supernova remnant1000 yr old supernova remnant
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NGC 6888 Crescent Nebula (Tony Hallas)NGC 6888 Crescent Nebula (Tony Hallas)
wind-blown bubble: stellar wind impact on its environmentwind-blown bubble: stellar wind impact on its environment
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Radiation-driven massive star Radiation-driven massive star windswinds
MM ~ 10 ~ 10-6-6 M Msunsun/yr/yr
Prinja et al. 1992, ApJ, 390, 266Prinja et al. 1992, ApJ, 390, 266
Velocity (km/s)Velocity (km/s)
v∞=2350 km/s
UV spectrum: C IV 1548, 1551 ÅUV spectrum: C IV 1548, 1551 Å
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Power in these winds:Power in these winds:
€
12 M
•
v∞2 ≈ 3×1036
≈ .001L∗
erg serg s-1-1
while the x-ray luminositywhile the x-ray luminosity
€
LX ≈10−7L∗
To account for the x-rays, only To account for the x-rays, only one part in 10one part in 10-4-4
of the wind’s mechanical power is needed to of the wind’s mechanical power is needed to heat the windheat the wind
LLsunsun = 4 x10 = 4 x103333 erg s erg s-1-1
LLmassivemassive ≈ 4 x10 ≈ 4 x103939
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Three models for massive star x-ray emissionThree models for massive star x-ray emission
1. Instability driven shocks1. Instability driven shocks
2. Magnetically channeled 2. Magnetically channeled wind shockswind shocks
3. Wind-wind interaction in 3. Wind-wind interaction in close binariesclose binaries
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Three models for massive star x-ray emissionThree models for massive star x-ray emission
1. Instability driven shocks1. Instability driven shocks
2. Magnetically channeled 2. Magnetically channeled wind shockswind shocks
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€
Γedd ≡FradFgrav
=κL
4πcGM
Winds of massive stars are driven by Winds of massive stars are driven by radiation pressureradiation pressure
luminosityluminosityopacityopacity
massmass
For the Sun, For the Sun, ΓΓedd edd ~ 10~ 10-5-5
For massive stars, For massive stars, ΓΓedd edd approaches unity approaches unity
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The Line-Driven Instability (LDI; Milne 1926)The Line-Driven Instability (LDI; Milne 1926)
€
v = v∞(1− R∗ /r)β
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Consider a positive velocity perturbationConsider a positive velocity perturbation
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Positive feedback: ion moves out of the Doppler shadow, Positive feedback: ion moves out of the Doppler shadow, sees more radiation, gets accelerated…sees more radiation, gets accelerated…
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1-D rad-hydro simulation of a massive star wind1-D rad-hydro simulation of a massive star wind
Radiation line driving is inherently unstable: Radiation line driving is inherently unstable: shock-heating and X-ray emissionshock-heating and X-ray emissionOwocki, Castor, & Rybicki 1988Owocki, Castor, & Rybicki 1988
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Predictions of the rad-hydro wind simulations:Predictions of the rad-hydro wind simulations:1.1. Significant Doppler broadening of x-ray emission Significant Doppler broadening of x-ray emission
lines due to bulk motion of the wind flow (1a. Shock lines due to bulk motion of the wind flow (1a. Shock onset several tenths Ronset several tenths R** above the surface) above the surface)
2.2. Bulk of the wind is cold and unshocked – source of Bulk of the wind is cold and unshocked – source of attenuation of the X-rays.attenuation of the X-rays.
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Puppis in the Gum NebulaPuppis in the Gum Nebula
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Puppis: 50 MPuppis: 50 Msunsun, 10, 106 6 LLsunsun
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PupPup
Chandra Chandra HETGS/MEG spectrum HETGS/MEG spectrum ((RR ~ 1000 ~ 300 km s ~ 1000 ~ 300 km s-1-1))
SiSi MgMg NeNe OOFeFe
H-likeH-likeHe-likeHe-like
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PupPup
Low-mass star (Capella) for comparisonLow-mass star (Capella) for comparison
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PupPup
CapellaCapella
Ne XNe X Ne IXNe IX Fe XVIIFe XVII
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PupPupmassivemassive
CapellaCapellalow masslow mass
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PupThe x-ray emission The x-ray emission lines are broad: lines are broad: agreement with rad agreement with rad hydro simulationshydro simulations
But… they’re also blue shifted and asymmetricBut… they’re also blue shifted and asymmetricIs this predicted by the wind shock scenario? Is this predicted by the wind shock scenario?
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€
τ∗≡κM
⋅
4πR∗v∞
opacity opacity of the cold of the cold wind componentwind component wind mass-loss ratewind mass-loss rate
wind terminal velocitywind terminal velocityradius of the starradius of the star
€
M•
= 4πr2vρ
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The basic wind-profile modelThe basic wind-profile modelτ=1,2,8
key parameters: key parameters: RRoo & & ττ**
€
τ∗≡κM
⋅
4πR∗v∞
j ~ 2 for r/R* > Ro,
= 0 otherwise
€
τ =τ∗R∗dz'
r'2 (1− R∗r ')β
z
∞
∫
Ro=1.5
Ro=3
Ro=10
ττ=1 contours=1 contours
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We fit these x-ray line profile models to each line in the We fit these x-ray line profile models to each line in the Chandra Chandra datadata
And find a best-fit And find a best-fit ττ** and and RRoo & place confidence limits on & place confidence limits on
these fitted parameter valuesthese fitted parameter values
Fe XVIIFe XVII 68, 90, 95% confidence limits68, 90, 95% confidence limits
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Wind opacity: photoelectric absorptionWind opacity: photoelectric absorption
Abundances; ionization balance; atomic cross sectionsAbundances; ionization balance; atomic cross sectionsVerner & Yakovlev 1996Verner & Yakovlev 1996
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Pup: three emission lines Pup: three emission lines
Mg LyMg Ly: 8.42 Å: 8.42 Å Ne LyNe Ly: 12.13 Å: 12.13 Å O LyO Ly: 18.97 Å: 18.97 Å
ττ** = 1 = 1 ττ** = 2 = 2 ττ** = 3 = 3
Recall: Recall:
€
τ∗≡κM
⋅
4πR∗v∞
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Fits to 16 lines in the Fits to 16 lines in the Chandra Chandra spectrum of spectrum of PupPup
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Traditional mass-loss rate: Traditional mass-loss rate: 8.3 X 108.3 X 10-6-6 Msun/yr Msun/yr
Our best fit: Our best fit: 3.5 X 103.5 X 10-6-6 Msun/yr Msun/yr
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Part 2: Magnetically Channeled WindsPart 2: Magnetically Channeled Winds
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The central star in the Orion Nebula Cluster - The central star in the Orion Nebula Cluster - 11 Ori C Ori C - is a - is a source of strong and relatively hard x-rayssource of strong and relatively hard x-rays
Chandra Chandra image: color coded by photon image: color coded by photon energy (red: <1keV; green 1 to 2 keV; energy (red: <1keV; green 1 to 2 keV; blue > 2 keV)blue > 2 keV)
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Recently discovered dipole magnetic field Recently discovered dipole magnetic field of > 1 kG : of > 1 kG : Zeeman Doppler spectroscopy (Wade et al. 2006)Zeeman Doppler spectroscopy (Wade et al. 2006)
Simulation/visualization courtesy R. TownsendSimulation/visualization courtesy R. TownsendMovie available at astro.swarthmore.edu/~cohen/presentations/apip09/Movie available at astro.swarthmore.edu/~cohen/presentations/apip09/rrm-o25-i75-b60-redt.avirrm-o25-i75-b60-redt.avi
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This field confines and channels the stellar wind out to This field confines and channels the stellar wind out to several stellar radii – several stellar radii –
what is the effect? what is the effect?
……MHD simulations (ZEUS, 2-D)MHD simulations (ZEUS, 2-D)
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Simulation/visualization courtesy A. ud-DoulaSimulation/visualization courtesy A. ud-DoulaMovie available at astro.swarthmore.edu/~cohen/presentations/apip09/Movie available at astro.swarthmore.edu/~cohen/presentations/apip09/ t1oc-lowvinf-logd.avit1oc-lowvinf-logd.avi
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Simulation/visualization courtesy A. ud-DoulaSimulation/visualization courtesy A. ud-DoulaMovie available at astro.swarthmore.edu/~cohen/presentations/apip09/Movie available at astro.swarthmore.edu/~cohen/presentations/apip09/ t1oc-lowvinf-logT.avit1oc-lowvinf-logT.avi
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Simulation/visualization courtesy A. ud-DoulaSimulation/visualization courtesy A. ud-DoulaMovie available at astro.swarthmore.edu/~cohen/presentations/apip09/Movie available at astro.swarthmore.edu/~cohen/presentations/apip09/ t1oc-lowvinf-speed.avit1oc-lowvinf-speed.avi
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temperaturetemperature emission measureemission measure
MHD simulations of magnetically channeled windMHD simulations of magnetically channeled wind
Channeled collision is close to head-on – Channeled collision is close to head-on – >1000 km s>1000 km s-1-1 : T > 10 : T > 1077 K K
simulations by A. ud-Doula; Gagné et al. (2005)simulations by A. ud-Doula; Gagné et al. (2005)
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Predictions: Predictions:
1.1.Shocks are strong – head-on – and so Shocks are strong – head-on – and so plasma is hotter;plasma is hotter;2.2.Hot plasma is moving much slower Hot plasma is moving much slower (confinement);(confinement);3.3.Rotational modulation of X-ray flux;Rotational modulation of X-ray flux;4.4.Hot plasma is ~1 RHot plasma is ~1 R** above the surface. above the surface.
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Pup
1 Ori C
ChandraChandra grating spectra grating spectra
11 Ori C: hotter plasma, narrower emission lines Ori C: hotter plasma, narrower emission lines
Pup: cooler plasma, broad emission linesPup: cooler plasma, broad emission lines
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Pup
1 Ori C
Si XIIISi XIVSi XIVMg XIMg XIMg XIIMg XII
H-likeH-like//He-like He-like ratio is temperature sensitiveratio is temperature sensitive
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Pup
1 Ori C
Si XIIISi XIVSi XIVMg XIMg XIMg XIIMg XII
The magnetic O star – The magnetic O star – 11 Ori C – is hotter Ori C – is hotter
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Differential emission measure Differential emission measure (temperature distribution)(temperature distribution)
MHD simulation of MHD simulation of 11 Ori C Ori C reproduces the observed reproduces the observed
differential emission measuredifferential emission measureWojdowski & Schulz (2005)Wojdowski & Schulz (2005)
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1000 km s-1
Emission lines Emission lines are are significantly narrower in significantly narrower in the magnetic massive the magnetic massive star’s x-ray spectrumstar’s x-ray spectrum
1 Ori C(O7 V)
Pup(O4 If)
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0.0
0.5
1.0
1.5
Sim
ulat
ion
EM
(10
56 c
m-3)
0.0
0.1
0.2
0.3
0.4
θ1 Ori
C A
CIS
-I c
ount
rat
e (s
-1)
0.0 0.2 0.4 0.6 0.8 1.0Rotational phase (P=15.422 days)
ChandraChandra broadband count rate vs. rotational phase broadband count rate vs. rotational phase
Model from MHD simulationModel from MHD simulation
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0.0
0.5
1.0
1.5
Sim
ulat
ion
EM
(10
56 c
m-3)
0.0
0.1
0.2
0.3
0.4
θ1 Ori
C A
CIS
-I c
ount
rat
e (s
-1)
0.0 0.2 0.4 0.6 0.8
1.0 Rotational phase (P=15.422 days)
The star itself occults the hot plasma torusThe star itself occults the hot plasma torus
The closer the The closer the hot plasma is to hot plasma is to
the star, the the star, the deeper the dip deeper the dip
in the x-ray light in the x-ray light curvecurve
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Emission measureEmission measure
contour encloses T > 10contour encloses T > 1066 K K
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Helium-like species’ forbidden-to-intercombination Helium-like species’ forbidden-to-intercombination line ratios – z/line ratios – z/(x+y) (x+y) – provide information about – provide information about the the location location of the hot plasma of the hot plasma
……not the not the densitydensity, as is usually the case. , as is usually the case.
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g.s. 1s2 1S
1s2s 3S1s2p 3P
1s2p 1P
resonance (w)
intercombination (x+y)forbidden (z)
10-20 eV
1-2 keV
Helium-like ions (e.g. OHelium-like ions (e.g. O+6+6, Ne, Ne+8+8, Mg, Mg+10+10, Si, Si+12+12, S, S+14+14) – ) – schematic energy level diagramschematic energy level diagram
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1s2s 3S
1s2p 3P1s2p 1P
resonance (w)
intercombination (x+y)forbidden (z)
g.s. 1s2 1S
Ultraviolet light from the star’s photosphere drives Ultraviolet light from the star’s photosphere drives photoexcitation out of the photoexcitation out of the 33S level S level
UV
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1s2s 3S
1s2p 3P1s2p 1P
resonance (w)
intercombination (x+y)forbidden (z)
g.s. 1s2 1S
The f/i ratio is thus a diagnostic of the local UV mean The f/i ratio is thus a diagnostic of the local UV mean intensity…intensity…
UV
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1s2s 3S
1s2p 3P1s2p 1P
resonance (w)
intercombination (x+y)forbidden (z)
g.s. 1s2 1S
……and thus the distance of the x-ray emitting plasma and thus the distance of the x-ray emitting plasma from the photospherefrom the photosphere
UV
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Model of f/i ratio dependence on dilution factor (radius)Model of f/i ratio dependence on dilution factor (radius)
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Rfir=1.2 R*
Rfir=4.0 R*
Rfir=2.1 R*
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He-like f/i ratios and the x-ray light curve both He-like f/i ratios and the x-ray light curve both indicate that the hot plasma is somewhat closer to indicate that the hot plasma is somewhat closer to
the photosphere than the MHD models predict. the photosphere than the MHD models predict.
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Conclusions
Normal massive stars have x-ray line profiles Normal massive stars have x-ray line profiles consistent with the predictions of the wind instability consistent with the predictions of the wind instability model.model.
Photoelectric absorptionPhotoelectric absorption’s effect on the profile shapes ’s effect on the profile shapes can be used as a mass-loss rate diagnostic: can be used as a mass-loss rate diagnostic: mass-mass-loss rates are lower than previously thoughtloss rates are lower than previously thought. .
Magnetic massive stars have harder spectra with Magnetic massive stars have harder spectra with narrower lines and rotationally modulated variability, in narrower lines and rotationally modulated variability, in general agreement with MHD simulations. general agreement with MHD simulations.
Line ratio Line ratio diagnostics are useful for localizing the hot diagnostics are useful for localizing the hot plasma, and indicate that the plasma, and indicate that the MHD simulations predict MHD simulations predict a location that is too far from the photospherea location that is too far from the photosphere. .