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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 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 X-Ray and Radio Connections 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 X-Ray and Radio Connections 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: OWR (LBV)WRSN •Winds evolve as the star evolves: X-Ray and Radio Connections Santa Fe, New Mexico, 3-6 Feb 2004 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 (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 Homunculus forms “mini”-Eruption Great Eruption X-Ray and Radio Connections Santa Fe, New Mexico, 3-6 Feb 2004 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) X-Ray and Radio Connections 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) X-Ray and Radio Connections Santa Fe, New Mexico, 3-6 Feb 2004 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) X-Ray and Radio Connections 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 X-Ray and Radio Connections 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 X-Ray and Radio Connections 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 X-Ray and Radio Connections 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 X-Ray and Radio Connections In eccentric orbit, intrinsic Lx a maximum at periastron Santa Fe, New Mexico, 3-6 Feb 2004 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 X-Ray and Radio Connections Santa Fe, New Mexico, 3-6 Feb 2004 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) X-Ray and Radio Connections Santa Fe, New Mexico, 3-6 Feb 2004 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) X-Ray and Radio Connections 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 X-Ray and Radio Connections Santa Fe, New Mexico, 3-6 Feb 2004 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? X-Ray and Radio Connections Santa Fe, New Mexico, 3-6 Feb 2004 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) • • • • X-Ray and Radio Connections Santa Fe, New Mexico, 3-6 Feb 2004 X-Ray and Radio Connections Santa Fe, New Mexico, 3-6 Feb 2004 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 X-Ray and Radio Connections 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