Multi-wavelength Observations of Colliding Stellar Winds Mike - - PowerPoint PPT Presentation

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multi wavelength observations of colliding stellar winds
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Multi-wavelength Observations of Colliding Stellar Winds Mike - - PowerPoint PPT Presentation

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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

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Santa Fe, New Mexico, 3-6 Feb 2004 X-Ray and Radio Connections

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)

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Santa Fe, New Mexico, 3-6 Feb 2004 X-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
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Santa Fe, New Mexico, 3-6 Feb 2004 X-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

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Santa Fe, New Mexico, 3-6 Feb 2004 X-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)

Flux Wavelength

P-Cygni profiles

V∞=(∆λ/λ)c

  • 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 X-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: O⇒WR (⇒LBV)⇒WR⇒SN
  • Winds evolve as the star evolves:
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Santa Fe, New Mexico, 3-6 Feb 2004 X-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
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Santa Fe, New Mexico, 3-6 Feb 2004 X-Ray and Radio Connections

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

Great Eruption Homunculus forms “mini”-Eruption

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Santa Fe, New Mexico, 3-6 Feb 2004 X-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

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Santa Fe, New Mexico, 3-6 Feb 2004 X-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

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Santa Fe, New Mexico, 3-6 Feb 2004 X-Ray and Radio Connections

The Stellar Emission

1992: 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) Inner:

  • ptically thick

thermal Outer:

  • ptically

thin thermal; NT? 3 cm. continuum (Duncan et al. 1995)

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Santa Fe, New Mexico, 3-6 Feb 2004 X-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
  • ptical, IR, radio and X-rays suggest periodically

varying emission: colliding winds?

  • one star or two?
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Santa Fe, New Mexico, 3-6 Feb 2004 X-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) 2.0 1.5 1.0 0.5 0.0 Phase 2004 2002 2000 1998 1996 1994

ROSAT ASCA

RXTE PCU2 L1 scaled data Chandra XMM-Newton

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Santa Fe, New Mexico, 3-6 Feb 2004 X-Ray and Radio Connections

Eta Car’s Latest Eclipse (June 29, 2003): Caught in the Act

40 30 20 10 Net PCU2 L1 counts s

  • 1

2.10 2.05 2.00 1.95 1.90 Orbital 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 17 May 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

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Santa Fe, New Mexico, 3-6 Feb 2004 X-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 )

2.10 2.05 2.00 1.95 1.90 1.85 1.80 Phase 35 30 25 20 15 10 5 PCU2 L1 rate (cts s

  • 1 )
Interval of Enhanced Absorption

Column 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

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Santa Fe, New Mexico, 3-6 Feb 2004 X-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 Net PCU2 counts s

  • 1

2004 2002 2000 1998 1996 Time (years) 150 100 50 Time to Next Flare (days) 2.0 1.8 1.6 1.4 1.2 1.0 0.8 Phase

PCU2 L1 Net rate PCU2 L1 Net rate (realtime data) "flares" Time to next X-ray Peak (days)

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Santa Fe, New Mexico, 3-6 Feb 2004 X-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 force balance determines which wind dominates 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

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Santa Fe, New Mexico, 3-6 Feb 2004 X-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

10 20 Distance (AU) 40 30 20 10

  • 10

Distance (AU)

To Earth

June 29,2003 Start of totality Dec 15 1997 End of totality Jan 23 1998 Recovery Mar 6 1998 1999 2000 2001 2002 Jan 2003 Feb 2003 Mar 2003 Apr 2003 May 2003 Jun 2003 Recovery from

  • ptical 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 Totality Sep 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) 2.0 1.5 1.0 0.5 0.0 Phase 2004 2002 2000 1998 1996 1994

ROSAT ASCA

RXTE PCU2 L1 scaled data Chandra XMM-Newton Model CWB curve

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Santa Fe, New Mexico, 3-6 Feb 2004 X-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
  • f the material flow in the shock, the location of the shock

between the stars, the orientation of the shock cone

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Santa Fe, New Mexico, 3-6 Feb 2004 X-Ray and Radio Connections

Comparison: Apastron vs. Quadrature

apastron quadrature

  • 20
  • 10
10 20 Distance (AU) 40 30 20 10
  • 10
Distance (AU) To Earth Start of totality Dec 15 1997/ Jun 27 2003? End of totality Jan 23 1998/Aug 5 2003? recovery Mar 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?
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Santa Fe, New Mexico, 3-6 Feb 2004 X-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)

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Santa Fe, New Mexico, 3-6 Feb 2004 X-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

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Santa Fe, New Mexico, 3-6 Feb 2004 X-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 θ1 Ori C?

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Santa Fe, New Mexico, 3-6 Feb 2004 X-Ray and Radio Connections

Conclusions

  • Colliding wind binary stars provide good laboratories for testing models
  • f 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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Santa Fe, New Mexico, 3-6 Feb 2004 X-Ray and Radio Connections

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Santa Fe, New Mexico, 3-6 Feb 2004 X-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
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Santa Fe, New Mexico, 3-6 Feb 2004 X-Ray and Radio Connections

Characteristics of Stellar Colliding Wind X-ray and Radio emission

X-ray Radio SED e- Acceleration shock heating Fermi acceleration Variability νchar 1GGHz (5keV) 5 GHz (0.02 neV) WR star τ(νchar)=1 radius few Rstar few 100 Rstar collisionally ionized plasma synchrotron emission (composite spectrum?) emission measure, luminosity, and absorbing column, not kT luminosity & absorption