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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

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

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

problems in measuring mass loss
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?

x rays as a probe of colliding wind systems
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
canonical examples of colliding wind binaries
“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


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
a brief history of eta car
A Brief History of Eta Car


V-Band Lightcurve






50 yrs


1820 1850 1880 1910 1940 1970 2000

An Eruptive Variable – what caused the Eruption?

panchromatic variability eta car
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)

wr 140 eta car 3d hydro models
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

structured mass loss eta car
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)

wr 140 historical x ray variability
WR 140: Historical X-ray Variability


ASCA: 1993-2000

ROSAT: 1990-1999


1983 – 1986

(Williams et al. 1990)

Courtesy A. Pollock

x ray spectrum eta car
X-ray Spectrum: Eta Car

Hot Component 50 MK


rxte breakthroughs
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

rxte wr140

RXTE lightcurve in the 2-10 keV band


eta car
Eta Car

…what happened in 2009?

eta car flare behavior
Eta Car Flare Behavior

... 1 AU Clumps?

color change near minimum wr 140
Color Change Near Minimum: WR 140

Hardness Ratio =(7.5-3 keV)/(7.5+3 keV)

3d lightcurve models wr 140
3D Lightcurve Models: WR 140

Modelling by C. Russell


3D Lightcurve Models: Eta Car

Okazaki et al. 2008

Parkin et al. 2008


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?)

eta car extended emission
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)

what shortened the 2009 minimum
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?

  • 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
thanks to the rxte team for 16 great years
Thanks to the RXTE Team for 16 Great Years!

esp. Evan Smith, heroic scheduler

colliding winds in wr 140
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

initial x ray results
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
direct imaging
Direct Imaging

VLBA imaging courtesy S Dougherty

what rxte sees
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)

rxte instrumentation
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
outstanding issues
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
rxte observations
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

the campaign
The Campaign


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

a sea change in mass loss rate
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)

3 d spectro models geometry of mass loss
3-D Spectro-Models: Geometry of Mass Loss

Courtesy T. Madura, Phd thesis


Synthetic Slit Spectra from 3-D SPH Sims



ω = 270°

ω = 90°

ω = 180°

Courtesy Tom Madura

ω = 0°

a coupled problem
A Coupled Problem:

(rotation? magnetic fields?)

Vink et al. 2001

Evolution effects mass loss

Mass loss effects evolution

lbv nebulae

Brandner et al.

D. F. Figer (UCLA) et al.,


Barlow et al. 1994

Post RSG?

Smith & Owocki 2006

LBV Nebulae
weight loss secrets of the stars
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…
colliding winds a simplified approach
Colliding Winds: A Simplified Approach

Early Work: Cherepashchuk (1976), Prilutskii & Usov (1976), Usov (1992), Steven, Blondin, Pollock (1992)





for Adiabatic shock, Lx  1/D(a, e)

Temps of 107K: Thermal X-ray Emission

cooling parameter

colliding winds as a means to mdot
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
reality is complicated hideki yukawa
“Reality is Complicated”– Hideki Yukawa

Importance of radiative instabilities at wind-wind interface (thin shell, etc, Parkin et al. 2009, Pittard & Corcoran 2002)

  • 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


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

results eta car
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?