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Observing Winds in Collision with RXTE

Observing Winds in Collision with RXTE. Michael F. Corcoran (CRESST/USRA/NASA-GSFC). With: B. Ishibashi (Nagoya) , T. Gull (NASA-GSFC), A. Damineli (IAGUSP), K. Hamaguchi (CRESST/UMBC/NASA-GSFC), A. F. J. Moffat (U. Montreal),

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Observing Winds in Collision with RXTE

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  1. Observing Winds in Collision with RXTE Michael F. Corcoran (CRESST/USRA/NASA-GSFC) With: B. Ishibashi (Nagoya), T. Gull (NASA-GSFC), A. Damineli (IAGUSP), K. Hamaguchi (CRESST/UMBC/NASA-GSFC), A. F. J. Moffat (U. Montreal), E. R. Parkin (ANU), A. M. T Pollock (ESA), J. M. Pittard (U. Leeds), Atsuo Okazaki (Hokkai-Gakuen University), S. P. Owocki (U. Delaware), C. M. P. Russell (U. Delaware) Weight-loss Secrets of the Biggest Stars

  2. Overview • Introduction: The complicated mass of massive stars • Colliding Wind Binaries: A shocking way to study mass loss • RXTE Breakthroughs • WR 140 • Eta Carinae • Conclusion

  3. Introduction: DM ~ M Mass is the fundamental stellar parameter, but as it increases it becomes (observationally) less well constrained; especially near the upper mass limit (~150 solar masses, Figer 2005) R145 in 30 Dor: M sin3i= 116+48 M (i =38° => M=300+125 M!) Schnurr et al 2009 Moffat 1989

  4. Problems In Measuring Mass Loss Winds: Smooth wind vs. clumped? (factor of a few overestimate); spherical or not? LBV eruptions: timescales & rates? SN explosion: core & remnant amounts?

  5. X-rays as a Probe of Colliding Wind Systems Wind velocities of 1000’s of km/s  X-ray emission • Solving the X-ray Lightcurve: • wind terminal velocities (i.e. escape velocities) through temperatures; wind acceleration • shock conditions & adiabatic/radiative cooling; flow dynamics from X-ray lines • density information via absorbing column measurements • D–1 variation – orbital elements and masses

  6. “Canonical” Examples of Colliding Wind Binaries • Two important “colliding wind binary shock laboratories”: • WR 140, a carbon-rich Wolf-Rayet star + a “normal” O-type companion in a peculiar orbit: 8 year period, eccentricity = 0.88 • Eta Carinae: an LBV + unseen companion, in a peculiar orbit: 5.5 year period, eccentricity ~ 0.9 • (Space Oddity: Both went through periastron passage within 5 days of each other in January 2009: next occurrence AD 12,620.808) RXTE has been key in defining the X-ray emitting shock properties vs. time

  7. WR 140 + Eta Car: Dynamical Sisters X-ray derived

  8. WR 140: “Canonical1” Massive Long Period Binary P. Williams • Coordinated variability at wavelengths from cm to 10-8 cm • all driven by wind-wind collision between the two stars

  9. A Brief History of Eta Car –1 V-Band Lightcurve 1 3 V 5 7 50 yrs 9 1820 1850 1880 1910 1940 1970 2000 An Eruptive Variable – what caused the Eruption?

  10. Panchromatic (?) Variability: Eta Car Radio variability (R. Duncan, S. White et al 1995) 1992 1993 Hard Soft • Periodic spectral variations in He I 10830A (Damineli 1996) and X-rays • strict period => gravitational dynamics X-rays (Corcoran et al. 1996)

  11. WR 140 + Eta Car: 3D Hydro models WR 140 Eta Carinae Simulations by E. R. Parkin, J. M. Pittard Two fast winds at different Mdots fast+slow wind at different Mdots

  12. Structured Mass Loss: Eta Car wind structure in orbital plane Density profile Okazaki et al. 2008 Bow shock shapes primary wind Variable r (NH) Coriolis distortions in wind near periastron passage effects photoionization of wind/nebula by the companion Thermalization of KE at WWC produces X-rays sensitive to orbit “Flashlight Effect”: variable illumination of the circumstellar material (See poster by T. Gull)

  13. WR 140: Historical X-ray Variability EXOSAT  ROSAT + ASCA  ASCA: 1993-2000 ROSAT: 1990-1999 EXOSAT: 1983 – 1986 (Williams et al. 1990) Courtesy A. Pollock

  14. X-ray Spectrum: Eta Car Hot Component 50 MK Fe XXV

  15. RXTE Breakthroughs: • Snapshot observations hampers detailed understanding • RXTE Observations of WR 140 and Eta Car provided: • Strongest evidence that Eta Car is a binary system • Adequate time sampling to separate phase-locked and secular trends in both systems • Detailed lightcurves to compare to models • New physical insights: clumping, radiative braking • Realistic wind structure and the “flashlight” effect • Surprises RXTE PCU observations: Eta Car: 1500 ksec Feb 9, 1996 - Dec 28, 2011 WR 140: 500 ksec Mar 3, 2001 - Dec 23, 2011

  16. RXTE: WR140 RXTE lightcurve in the 2-10 keV band “Historical”

  17. RXTE: Eta Car 2-10 keV

  18. Comparison of Periastra: WR140

  19. Eta Car …what happened in 2009?

  20. Eta Car Flare Behavior ... 1 AU Clumps?

  21. Color Change: WR 140

  22. Color Change Near Minimum: WR 140 Hardness Ratio =(7.5-3 keV)/(7.5+3 keV)

  23. Color Change Near Minimum: Eta Car

  24. 3D Lightcurve Models: WR 140 Modelling by C. Russell

  25. 3D Lightcurve Models: Eta Car Okazaki et al. 2008 Parkin et al. 2008 =270-w 3-D SPH + Isothermal point source emission 3-D Hydro + extended emission via 2-D hydro Duration of X-ray minimum suggests collapse of shock (radiative braking? radiative inhibition?)

  26. Eta Car: Extended Emission? Post-Periastron “Hot Bubble” due to fast companion wind colliding with swept-up wall of the LBV wind reduces minimum depth, duration... (Russell et al. 2011)

  27. What Shortened the 2009 Minimum? • Minimum depends on: • intrinsic 2-10 keV emission of shock near periastron (radiative instabilities important) • amount of absorption around the “bubble” A decrease in the LBV’s mass loss rate could make the shock less radiative (more stable) and less absorbed  shorter X-ray Minimum? Or something Else?

  28. Summary • Studies of the colliding winds in systems like WR140 and Eta Car in X-rays (and UV, optical, IR & radio) provide unique information regarding mass loss in extremely massive stars, and information on behavior of astrophysical shocks • Detailed modeling of the wind-shock boundary shape and flow • Relative mass-loss pressure ratio (in-situ density diagnostics; clumping independent?) • Dynamical studies (and periastron triggers?) • Dust generation from shocked gas • Detailed lab shock-physics experiments with varying conditions/parameters

  29. Thanks to the RXTE Team for 16 Great Years! esp. Evan Smith, heroic scheduler

  30. Colliding Winds in WR 140 Wind-Wind collisions in WR 140 allow us to probe time-variable shock physics under conditions of densities and temperatures which are difficult to reproduce on Earth WR140: Our Shock Physics Laboratory Courtesy P. Williams

  31. Initial X-ray Results • Bright, variable X-ray source (unusual for a single massive star, even more unusual for a single WR star) • Variable X-ray spectrum: Changes in emission measure of the hot gas, absorption to the hot gas • Hard source: kT ~ 3-4 keV (also unusual for single massive star) • Need Detailed Monitoring: • the Rossi X-ray Timing Explorer

  32. Direct Imaging VLBA imaging courtesy S Dougherty

  33. What RXTE Sees: Optical: Crowded Stellar Field X-ray: WR 140 dominant source Dominated by WR140 CW emission above 2 keV RASS 2x2 degree image of WR 140, 0.5-2 keV (with RXTE 5%, 30% & 80% contours)

  34. RXTE Instrumentation • RXTE has 3 instruments: • The Proportional Counter Array (PCA): • a set of five collimated Xenon-filled proportional counter units • 2-70 keV; 1600 cm2 • Most useful for WR 140 • The High Energy X-ray Timing Experiment (HEXTE) • two clusters of 4 NaI/CsI scintillator detectors • 15-250 keV; 1600 cm2 • The All-Sky Monitor (ASM) • 3 shadow cameras; 90 cm2

  35. Outstanding Issues • Cause of the “Event” (eclipse; cooling/“discombobulation”; phase-dependent mdot? Jet formation?) • Stability of the bow shock • Interactions near periastron • Geometry of the inner/outer wind • Density profile of the inner wind of Eta Car • Radial velocities & mass ratio • Goals: • 3-D Reconstruction of mass outflows, ejecta, photon fields • Use the orbit of the companion as a probe of the fundamental parameters of Eta Car

  36. RXTE Observations RXTE started observing 2-10 keV emission from Eta Car shortly after launch in Feb 1996 Continued monitoring with daily/weekly/monthly cadence since then Daily monitoring near X-ray minima

  37. The Campaign Swift P=2024 d; e~0.9; a~15 AU; i~50o Ishibashi et al. 1998; Corcoran et al. 2001 Simulations by A. Okazaki The Event

  38. A (Sea) Change in Mass Loss Rate STIS, Gemini reveal weakening of emission lines in 2009 (Mehner et al. 2010) Large decrease in Mdot from LBV? Decrease in Mdot may also explain the decrease in duration of X-ray minimum ( See C. Russell, Poster P5.20; Kashi & Soker 2009)

  39. 3-D Spectro-Models: Geometry of Mass Loss Courtesy T. Madura, Phd thesis

  40. Synthetic Slit Spectra from 3-D SPH Sims MODEL STIS ω = 270° ω = 90° ω = 180° Courtesy Tom Madura ω = 0°

  41. A Coupled Problem: (rotation? magnetic fields?) Vink et al. 2001 Evolution effects mass loss Mass loss effects evolution

  42. Brandner et al. D. F. Figer (UCLA) et al., NICMOS, HST, NASA, Barlow et al. 1994 Post RSG? Smith & Owocki 2006 LBV Nebulae

  43. Weight Loss Secrets of the Stars For the most massive star, mass loss makes it difficult to measure masses Mass Loss History • Mass is lost due to • radiatively driven stellar winds • Transfer/Roche Lobe leaks • Eruptions • Explosions…

  44. Colliding Winds: A Simplified Approach Early Work: Cherepashchuk (1976), Prilutskii & Usov (1976), Usov (1992), Steven, Blondin, Pollock (1992) c>1: adiabatic c<1: radiative for Adiabatic shock, Lx  1/D(a, e) Temps of 107K: Thermal X-ray Emission cooling parameter

  45. Colliding Winds as a Means to Mdot • Stellar winds will hit something: • Interstellar medium • another star • wind from another star • Colliding wind Binaries provide: • – in-situ probe of mass loss • – “Clumping-free” estimator? (Pittard 2007) • – way to probe the stellar parameters • – “laboratory” physics of astrophysical hypersonic shocks

  46. “Reality is Complicated”– Hideki Yukawa Importance of radiative instabilities at wind-wind interface (thin shell, etc, Parkin et al. 2009, Pittard & Corcoran 2002)

  47. Results • Point source approximation near periastron can reproduce minimum • More realistic distribution of hot gas along the shock boundary (“extended emission model”) does notreproduce the X-ray minimum as well… • radiative cooling near periastron vs. adiabatic cooling near apastron? • shift in X-ray temperature near periastron? §assuming V∞=2.5 Vesc

  48. Eta Carinae

  49. optical & X-ray h Car is one of the most luminous (massive) stars in the Galaxy (most luminous, massive star within 3 kpc.) Hubble Mosaic of the Carinae Nebula

  50. Results: Eta Car • Point source approximation near periastron can reproduce depth of minimum • More realistic distribution of hot gas along the shock boundary (“extended emission model”) does not reproduce the X-ray minimum as well… • radiative cooling near periastron vs. adiabatic cooling near apastron? • shift in X-ray temperature near periastron?

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