Santa Fe, New Mexico, 3-6 Feb 2004X-Ray and Radio Connections Multi-wavelength Observations of...
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Transcript of Santa Fe, New Mexico, 3-6 Feb 2004X-Ray and Radio Connections Multi-wavelength Observations of...
Santa Fe, New Mexico, 3-6 Feb 2004X-Ray and Radio Connections
Multi-wavelength Observations of Colliding
Stellar Winds
Mike CorcoranUniversities Space Research Association
andNASA/GSFC Laboratory for High Energy Astrophysics
Collaborators:
Julian Pittard (Leeds)
Ian Stevens (U. Birmingham)
David Henley (U. Birmingham)
Andy Pollock (ESA)
Santa Fe, New Mexico, 3-6 Feb 2004X-Ray and Radio Connections
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
Santa Fe, New Mexico, 3-6 Feb 2004X-Ray and Radio Connections
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
Santa Fe, New Mexico, 3-6 Feb 2004X-Ray and Radio Connections
Massive Stars (10<M/M<100): Colliding Wind Labs
• Wind parameters (mass loss rates, wind velocities) can be characterized (UV, radio)
Flu
x
Wavelength
P-Cygni profiles
V(c
•Stellar parameters (masses, temperatures, radii, rotational velocity) can often be estimated
•They are nearby
•Generate X-ray & Radio emission
Santa Fe, New Mexico, 3-6 Feb 2004X-Ray and Radio Connections
Stellar Wind Characteristics• For Massive Stars Near the Main Sequence
•Lots of energy to accelerate particles and heat gas•Evolutionary scenario: OWR (LBV)WRSN•Winds evolve as the star evolves:
Santa Fe, New Mexico, 3-6 Feb 2004X-Ray and Radio Connections
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
Santa Fe, New Mexico, 3-6 Feb 2004X-Ray and Radio Connections
A (non)canonical example: Eta Carinae
• Eta Car: perhaps the Galaxy’s most massive & luminous star (5106 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
Great Eruption
Homunculus forms
“mini”-Eruption
Santa Fe, New Mexico, 3-6 Feb 2004X-Ray and Radio Connections
Humphrey and Davidson 1994
Eta Car and the Homunculus
The Star
HST/ACS image of Eta Car (Courtesy the HST TREASURY PROJECT)
the Paddle
The Skirt
the “jet”
Lobes
Artist rendering of Eta Carina based on Very Large Telescope Interferometer (ESO) observations
Santa Fe, New Mexico, 3-6 Feb 2004X-Ray and Radio Connections
Eta Car: From the Outside In
HST/WFPC2 [N II] 6583 (courtesy N. Smith)
E Condensations
S Ridge
W condensations
Homunculus
“Jet”
“Strings”
The Outer Ejecta
Outer debris ejected a few hundred years before the Great Eruption
shocks from ejecta/CSM collision
Santa Fe, New Mexico, 3-6 Feb 2004X-Ray and Radio Connections
The Stellar Emission1992: contemporaneous radio & X-ray observations saw a rapid brightening of the star
92 Jun 93 Jan
0.5-1.0 keV
E>1.6 keV
1 arcmin.
X-ray continuum (Corcoran et al. 1995)3 cm. continuum (Duncan et al. 1995)
Inner: optically thick thermal
Outer: optically thin thermal; NT?
Santa Fe, New Mexico, 3-6 Feb 2004X-Ray and Radio Connections
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?
Santa Fe, New Mexico, 3-6 Feb 2004X-Ray and Radio Connections
Radio and X-ray Monitoring of Eta Car
3.0x10-10
2.5
2.0
1.5
1.0
0.5
0.0
Observed Flux (2-10 keV)
2.01.51.00.50.0
Phase
200420022000199819961994
ROSAT
ASCA
RXTE PCU2 L1 scaled data Chandra XMM-Newton
Santa Fe, New Mexico, 3-6 Feb 2004X-Ray and Radio Connections
Eta Car’s Latest Eclipse (June 29, 2003): Caught in the Act
40
30
20
10
0
Net PCU2 L1 counts s
-1
2.102.052.001.951.90Orbital Phase
June 29
INTEGRAL
XMM
End of XMM Visibility
PCU2 L1 net counts PCU2 L1 net counts from quicklook data Previous cycle
"Flares"
previous cycle
May 17May 26
June 15
Around the time of the X-ray eclipse, snapshot monitoring of Eta Car’s X-ray emission by Chandra and the XMM-Newton X-ray Observatories
Nov 20 2000 Oct 16 2002 May 3 2003 Jun 16 2003 Jul 20 2003 Sep 26 2003
Santa Fe, New Mexico, 3-6 Feb 2004X-Ray and Radio Connections
Absorption variations
Variation of X-ray spectrum from XMM-Newton observations
25
20
15
10
5
NH
(10
22
cm
-2)
2.102.052.001.951.901.851.80
Phase
35
30
25
20
15
10
5
PCU2 L1 rate (cts s
-1)
Interval of Enhanced AbsorptionColumn Densities Chandra XMM-Newton SAX (from previous cycle) ASCA (from previous cycle) RXTE
PCU2 L1 rate
Variation of observed X-ray flux and column density during 2003 X-ray minimum
Santa Fe, New Mexico, 3-6 Feb 2004X-Ray and Radio Connections
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
Red points show the time between X-ray peaks.
40
30
20
10
0
Net PCU2 counts s
-1
20042002200019981996
Time (years)
150
100
50
0
Time to Next Flare (days)
2.01.81.61.41.21.00.8
Phase
PCU2 L1 Net rate PCU2 L1 Net rate (realtime data) "flares" Time to next X-ray Peak (days)
Santa Fe, New Mexico, 3-6 Feb 2004X-Ray and Radio Connections
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
Intrinsic X-ray luminosity varies the square of the density x volume
Observed flux is proportional to intrinsic flux modified by absorption
cooler
hotter
slow dense wind fast thin wind In eccentric orbit, intrinsic Lx a maximum at periastron
force balance determines which wind dominates
Santa Fe, New Mexico, 3-6 Feb 2004X-Ray and Radio Connections
Comparisons to the Simple Model
• General trends are reproduced; details (secular increases in Lx, short-period variability) not
• requires extra absorption to match width of minimum
-20
-10
0
10
20
Distance (AU)
403020100-10
Distance (AU)
To Earth
June 29,2003
Start of totalityDec 15 1997
End of totalityJan 23 1998
RecoveryMar 6 1998
1999
2000
2001
2002
Jan 2003
Feb 2003
Mar 2003
Apr 2003
May 2003
Jun 2003
Recovery from optical minimum
Orbit of Secondary relative to Primary (based on elements in Corcoran et al. 2001)
1997 Maximum (Nov 9)
2003 Maximum (May26)
July 12, 2003
End of TotalitySep 10 2003
Recovery Sep 23, 2003
Derived orbit of companion around Eta Car, based on the model lightcurve
3.0x10-10
2.5
2.0
1.5
1.0
0.5
0.0
Observed Flux (2-10 keV)
2.01.51.00.50.0
Phase
200420022000199819961994
ROSAT
ASCA
RXTE PCU2 L1 scaled data Chandra XMM-Newton Model CWB curve
Santa Fe, New Mexico, 3-6 Feb 2004X-Ray and Radio Connections
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
Santa Fe, New Mexico, 3-6 Feb 2004X-Ray and Radio Connections
Comparison: Apastron vs. Quadrature
apastronquadrature
-20
-10
0
10
20
Distance (AU)
403020100-10
Distance (AU)
To Earth
Start of totalityDec 15 1997/ Jun 27 2003?
End of totalityJan 23 1998/Aug 5 2003?
recoveryMar 6 1998/ Sep 16 2003?
1999
2000
2001
2002
Jan 2003
Feb 2003
Mar 2003
Apr 2003
May 2003
Jun 2003
Orbit of Secondary relative to Primary (based on elements in Corcoran et al. 2001)
1997 Maximum (Nov 9)
2003 Maximum? (May31)
July 12, 2003
• Decrease in f/i ratio• broader, double-peaked lines• Doppler shifts?
Santa Fe, New Mexico, 3-6 Feb 2004X-Ray and Radio Connections
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) Pittard et al. (2002)
Santa Fe, New Mexico, 3-6 Feb 2004X-Ray and Radio Connections
Resolving Confusion in The Trifid Nebula
Rho et al. 2001
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. 2004
Santa Fe, New Mexico, 3-6 Feb 2004X-Ray and Radio Connections
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?
Santa Fe, New Mexico, 3-6 Feb 2004X-Ray and Radio Connections
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)
Santa Fe, New Mexico, 3-6 Feb 2004X-Ray and Radio Connections
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
Santa Fe, New Mexico, 3-6 Feb 2004X-Ray and Radio Connections
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, and absorbing column, not kT
luminosity & absorption
char 1GGHz (5keV) 5 GHz (0.02 neV)
WR star (char)=1 radius
few Rstar few 100 Rstar