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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

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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 eta car dynamical sisters

    WR 140 + Eta Car: Dynamical Sisters

    X-ray derived

    Observing winds in collision with rxte

    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

    Fe XXV

    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: WR140

    RXTE lightcurve in the 2-10 keV band


    Rxte eta car

    RXTE: Eta Car

    2-10 keV

    Comparison of periastra wr140

    Comparison of Periastra: WR140

    Eta car

    Eta Car

    …what happened in 2009?

    Eta car flare behavior

    Eta Car Flare Behavior

    ... 1 AU Clumps?

    Color change wr 140

    Color Change: WR 140

    Color change near minimum wr 140

    Color Change Near Minimum: WR 140

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

    Color change near minimum eta car

    Color Change Near Minimum: Eta Car

    3d lightcurve models wr 140

    3D Lightcurve Models: WR 140

    Modelling by C. Russell

    Observing winds in collision with rxte

    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

    Observing winds in collision with rxte

    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

    Eta carinae

    Eta Carinae

    Observing winds in collision with rxte

    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?

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