Download ppt 2.6 - NRAO: Socorro, New Mexico

Multi-wavelength Observations of
Colliding Stellar Winds
Mike Corcoran
Universities Space Research Association
and
NASA/GSFC Laboratory for High Energy Astrophysics
Collaborators:
Julian Pittard (Leeds)
Ian Stevens (U. Birmingham)
David Henley (U. Birmingham)
Andy Pollock (ESA)
X-Ray and Radio Connections
Santa Fe, New Mexico, 3-6 Feb 2004
Outline of Talk
• Statement of the Problem
• Massive Stars as Colliding Wind Labs
– Wind Characteristics
– Types of Interactions
•
•
•
•
A (non) canonical Example: Eta Car
New high resolution tools
Colliding winds in Single Stars
Conclusions
X-Ray and Radio Connections
Santa Fe, New Mexico, 3-6 Feb 2004
Statement of a General Problem:
• An “engine” loses mass into its surroundings
• the surroundings are “messy” and the outflow collides with
nearby “stuff”
• by observing the results of this collision, we can learn about the
engine, its environment, and the relation between the engine
and the environment
• Concentrate on: Massive outflows from massive (non-exploding)
stars
• neglect interesting phenomena like magneto-hydrodynamic
interactions in winds of lower mass stars and AGB
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Santa Fe, New Mexico, 3-6 Feb 2004
Massive Stars (10<M/M<100): Colliding Wind Labs
• Wind parameters (mass loss rates, wind velocities) can be
characterized (UV, radio)
Flux
P-Cygni profiles
V(Dl/l)c
Wavelength
•Stellar parameters (masses, temperatures, radii, rotational
velocity) can often be estimated
•They are nearby
•Generate X-ray & Radio emission
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Santa Fe, New Mexico, 3-6 Feb 2004
Stellar Wind Characteristics
• For Massive Stars Near the Main Sequence
•Lots of energy to accelerate particles and heat gas
•Evolutionary scenario: OWR (LBV)WRSN
•Winds evolve as the star evolves:
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Types of Interactions:
• Stellar outflows can collide with
–
–
–
–
–
pre-existing clouds
earlier ejecta
winds from a companion
a companion
itself
• All these collisions can produce observable emission from
shocked gas
• Typical velocities 100-1000 km/s  T ~ 106 K
X-Ray and Radio Connections
Santa Fe, New Mexico, 3-6 Feb 2004
A (non)canonical example:
Eta Carinae
• Eta Car: perhaps the Galaxy’s most massive & luminous star
(5106 L ; 100 M ; cf. the Pistol Star, LBV1806-20)
• An eruptive star (erupted in 1843; 1890; 1930?; now?)
• shows beautiful ejecta: outer debris field and the “Homunculus”
nebula
Homunculus forms
“mini”-Eruption
Great Eruption
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Eta Car and
the Homunculus
the Paddle
Humphrey and Davidson 1994
The Skirt
The Star
the “jet”
Lobes
HST/ACS image of Eta Car (Courtesy the HST TREASURY PROJECT)
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Santa Fe, New Mexico, 3-6 Feb 2004
Artist rendering of Eta Carina based on
Very Large Telescope Interferometer
(ESO) observations
Eta Car: From the Outside In
The Outer Ejecta
Outer debris
ejected a few
hundred years
before the Great
Eruption
shocks from
ejecta/CSM
collision
W condensations
“Jet”
Homunculus
S Ridge
E Condensations
“Strings”
HST/WFPC2 [N II] 6583 (courtesy N. Smith)
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The Stellar Emission
1992: contemporaneous radio & X-ray observations
saw a rapid brightening of the star
92 Jun
93 Jan
Inner:
optically thick
thermal
0.5-1.0 keV
1 arcmin.
Outer:
optically
thin
thermal;
NT?
E>1.6 keV
3 cm. continuum (Duncan et al. 1995)
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X-ray continuum (Corcoran et al. 1995)
Santa Fe, New Mexico, 3-6 Feb 2004
Continued Variability
• Monitoring since 1992 in radio and X-ray regimes
showed continuous variability
• Damineli (1996) showed evidence of a 5.5 year
period from ground-based spectra
• apparent simultaneous variations in ground-based
optical, IR, radio and X-rays suggest periodically
varying emission: colliding winds?
• one star or two?
X-Ray and Radio Connections
Santa Fe, New Mexico, 3-6 Feb 2004
Radio and X-ray Monitoring of Eta Car
Observed Flux (2-10 keV)
3.0x10
1994
-10
1996
1998
2000
2002
2004
RXTE PCU2 L1 sc aled data
Chandra
XMM-Newton
2.5
2.0
1.5
ROSAT
1.0
0.5
ASCA
0.0
0.0
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0.5
1.0
Phase
1.5
Santa Fe, New Mexico, 3-6 Feb 2004
2.0
Eta Car’s Latest Eclipse (June 29, 2003): Caught in the Act
40
May 17
Around the time of the Xray eclipse, snapshot
monitoring of Eta Car’s Xray emission by Chandra
and the XMM-Newton Xray Observatories
May 26
PCU2 L1 net counts
PCU2 L1 net counts from quicklook dat a
Previous cycle
"Flares"
June 15
30
Net PCU2 L1 counts s
-1
End of XMM Visibility
20
XMM
10
June 29
previous cycle
INTEGRAL
0
1.90
1.95
2.00
2.05
2.10
Orbital Phase
Nov 20 2000
Oct 16 2002
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May 3 2003
Jun 16 2003
Santa Fe, New Mexico, 3-6 Feb 2004
Jul 20 2003
Sep 26 2003
Absorption variations
35
25
Column Densities
Chandra
XMM-Newton
SAX (from previous cycle)
ASCA (from previous cycle)
RXTE
Interval of Enhanced Absorption
30
cm
-2
)
PCU2 L1 rate
NH (10
22
20
15
-1
15
PCU2 L1 rate (cts s
25
20
)
10
10
5
1.80
5
1.85
1.90
1.95
2.00
2.05
2.10
Phase
Variation of X-ray spectrum from XMM-Newton observations
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Santa Fe, New Mexico, 3-6 Feb 2004
Variation of observed X-ray
flux and column density
during 2003 X-ray minimum
X-ray “flares”
•
Frequent monitoring of the X-ray flux of Eta Car with RXTE showed
unexpected quasi-periodic spikes occurring ~every 3 months
get stronger and more frequent on approach to X-ray minimum
•
Phase
0.8
1.0
1.2
1.4
1.6
1.8
2.0
40
PCU2 L1 Net rate
PCU2 L1 Net rate (realtime data)
"flares"
Time to next X-ray Peak (days)
150
-1
Net PCU2 counts s
100
20
50
10
0
1996
0
1998
2000
2002
Time (years)
Red points show the time between X-ray peaks.
X-Ray and Radio Connections
Santa Fe, New Mexico, 3-6 Feb 2004
2004
Time to Next Flare (days)
30
A Simple CWB Model
• X-rays are generated in the shock where the massive, slow wind from Eta Car
smashes into and overcomes the thin, fast wind from the companion
force balance determines which wind
dominates
Intrinsic X-ray luminosity varies
the square of the density x volume
cooler
Observed flux is proportional to
intrinsic flux modified by
absorption
hotter
slow dense wind
fast thin wind
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In eccentric orbit, intrinsic Lx a maximum at
periastron
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Comparisons to the Simple Model
1994
-10
1996
1998
2000
2002
2004
RXTE PCU2 L1 scaled data
Chandra
XMM-Newton
Model CWB curve
2.5
2.0
1.5
ROSAT
1.0
May 2003
20
Apr 2003
0.5
Start of totality
Dec 15 1997
ASCA
0.0
10
0.0
0.5
1.0
Phase
1.5
Mar 2003
Jun 2003
Feb 2003
Jan 2003
June 29,2003
2.0
2002
Distance (AU)
Observed Flux (2-10 keV)
3.0x10
1997 Maximum (Nov 9)
0
2001
2003 Maximum (May26)
July 12, 2003
To Earth
Recovery from
optical minimum
• General trends are reproduced;
details (secular increases in Lx,
short-period variability) not
• requires extra absorption to match
width of minimum
X-Ray and Radio Connections
2000
-10
1999
Recovery
Sep 23, 2003
End of totality
Jan 23 1998
End of Totality
Sep 10 2003
-20
Recovery
Mar 6 1998
Orbit of Secondary relative to Primary
(based on elements in Corcoran et al. 2001)
-10
0
10
20
30
Distance (AU)
Derived orbit of companion around
Eta Car, based on the model lightcurve
Santa Fe, New Mexico, 3-6 Feb 2004
40
X-ray Grating Spectroscopy: Measuring the Flow
Geometry
• Nearby CWB systems are bright enough for X-ray grating
spectroscopy
• line diagnostics (width, centroids, ratios) measure characteristics
of the material flow in the shock, the location of the shock
between the stars, the orientation of the shock cone
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Comparison: Apastron vs. Quadrature
apastron
quadrature
May 2003
20
Apr 2003
• Decrease in f/i ratio
• broader, double-peaked
lines
• Doppler shifts?
Mar 2003
Start of totality
Jun 2003
Dec 15 1997/ Jun 27 2003?
Feb 2003
Jan 2003
10
Distance (AU)
2002
1997 Maximum (Nov 9)
0
2001
2003 Maximum? (May31)
July 12, 2003
To Earth
2000
-10
1999
End of totality
Jan 23 1998/Aug 5 2003?
recovery
Mar 6 1998/ Sep 16 2003?
-20
Orbit of Secondary relative to Primary
(based on elements in Corcoran et al. 2001)
-10
0
10
20
30
40
Distance (AU)
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Spatial Morphology (1):
Resolving the shock structure
WR 146, WR 147: composite radio spectra, have been resolved in the
radio, NT emission from a bow shock
NT
bow shock
Thermal WR147 wind
WR 147: Williams et al (1997)
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Pittard et al. (2002)
Santa Fe, New Mexico, 3-6 Feb 2004
Resolving Confusion in The Trifid Nebula
Rho et al. 2004
HD 164492A (O7.5III)
ionizes the nebula
ROSAT & ASCA found
a bright hard source
coincident with the star
…but Chandra resolved the O star as a soft
source; hard source is an optically faint object
to the south
Rho et al. 2001
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Self-Colliding Winds
•
Radiatively driven winds intrinsically unstable to doppler perturbations
(Lucy & Solomon 1970; Feldmeier 1998). Shocks can form and
produce observable emission
– X-rays: soft, non-variable
– NT radio?
•
Dipolar magnetic field (few hundred G at surface) embedded in a wind
can produce magnetically confined wind shock (Babel & Montmerle
1997)
– rotationally modulated
– hard emission
– explains 1 Ori C?
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Conclusions
•
Colliding wind binary stars provide good laboratories for testing models
of shock-generated radio & X-ray emission
•
Studies of CW emission provide unique information about the densities,
temperature ranges and structure of the interaction region
Detailed timing, spectral and imaging studies suggest shocks and
winds are not smooth and homogeneous
shape, stability and aberration of the shock cone important
X-ray line profile variability can reveal details about the geometry and
dynamics of the outflow
Presence of hard X-ray emission and/or NT radio emission from
unconfused sources may be a good indicator of a companion (and
hence a good probe of the binary fraction for long-period systems)
•
•
•
•
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Spatial Morphology (2): Source Identification
• Most single stars are low-energy (soft) X-ray sources (little
emission above 2 keV)
• Use detection of 2 keV emission to ID (separated) binaries,
improve knowledge of binary fraction
• cf. Dougherty & Williams (2000): identify binaries from NT
emission?
• caveat: source confusion
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Santa Fe, New Mexico, 3-6 Feb 2004
Characteristics of Stellar Colliding Wind X-ray and Radio
emission
X-ray
Radio
SED
collisionally ionized plasma
synchrotron emission
(composite spectrum?)
e- Acceleration
shock heating
Fermi acceleration
Variability
emission measure, luminosity, luminosity & absorption
and absorbing column, not kT
nchar
1GGHz (5keV)
5 GHz (0.02 neV)
WR star t(nchar)=1
radius
few Rstar
few 100 Rstar
X-Ray and Radio Connections
Santa Fe, New Mexico, 3-6 Feb 2004