Physics and Dynamics of X-ray Plasma in Hot Stars
A.M.T. Pollock
RGS Calibration Scientist
European Space Agency, XMM-Newton Science Operations Centre,
European Space Astronomy Centre, 28080 Madrid, España
Cassinelli,
Cohen, Corcoran, Feldmeier, Gagné, Ignace, Henley, Leutenegger, MacFarlane,
Miller, Oskinova, Owocki, Raassen, Schulz, Skinner, Walborn,
Waldron.
X-ray Grating Spectroscopy, Cambridge MA, 2007 July 11-13
High-Resolution X-rays from Hot Stars
Andy Pollock
XMM-Newton SOC
European Space Astronomy Centre
Villafranca del Castillo, Madrid, Spain
The X-ray spectrum of  Puppis O4I
• lines resolved
• no flat tops
• He-like(fi(UV))
• weak continuum
High-Resolution X-rays from Hot Stars
Andy Pollock
XMM-Newton SOC
European Space Astronomy Centre
Villafranca del Castillo, Madrid, Spain
The line-driven winds of hot stars
Ý  4 r 2 (r)v(r)
M
v(r)  v (1 R* / r) 
LX/Lbol~10-7

X-rays from instabilities in the
acceleration zone à la Lucy &
White (1980) et seq.
¿ X() ?
¿ wind clumping ?
¿ mass-loss rates ?
Vela X-1 test
High-Resolution X-rays from Hot Stars
Andy Pollock
XMM-Newton SOC
European Space Astronomy Centre
Villafranca del Castillo, Madrid, Spain
The physics involved
• Shocks (cf SNRs)
• collisionless
• plasma driven
• post-shock relaxation
• Plasma physics
• Equilibrium - yes or no ?
• T  f(v)dv
• Gas dynamics
• X-ray absorption in clumpy media
• Chemical abundances
• Magnetic fields
• Consequences for current models
• line-driven instability shocks in single stars
• numerical hydrodynamic simulations of colliding-wind binaries (CWBs)
High-Resolution X-rays from Hot Stars
Andy Pollock
XMM-Newton SOC
European Space Astronomy Centre
Villafranca del Castillo, Madrid, Spain
The high-resolution X-ray sample
• instrinsic X-rays
• O2-O9-B0 I-V
• WN2-8
• WC4-WC9
• LBV
• magnetic stars
• colliding-wind binaries
• ISM
High-Resolution X-rays from Hot Stars
Andy Pollock
XMM-Newton SOC
European Space Astronomy Centre
Villafranca del Castillo, Madrid, Spain
X-ray spectra of O stars
 Ori
LineProfile(!)
 Cohen+ (2006) moments
 Oskinova+ (2006) clumps
 Pollock (2007) TriLines
 Waldron & Cassinelli (2007)
High-Resolution X-rays from Hot Stars
Andy Pollock
XMM-Newton SOC
European Space Astronomy Centre
Villafranca del Castillo, Madrid, Spain
Stacked X-ray line profiles of single O stars
High-Resolution X-rays from Hot Stars
Andy Pollock
XMM-Newton SOC
European Space Astronomy Centre
Villafranca del Castillo, Madrid, Spain
Chandra MEG stacked profiles of more OB stars
TriLine velocities (km/s)
blueV
centralV
redV
 Pup
-2068
-829
+1937
 Per
-2180
-408
+2488
 Ori
-1585
-303
+1723
 Ori
-1495
-251
+1480
 Ori
-1613
-78
+1675
 Ori
-552
-94
+517
 Oph
-1055
-27
+787
 Ori
-2113
-44
+2262
 the single TriLine profile is OK for all the lines in these OB stars
 disagreement with Miller+ (2002) for  Ori
 disagreement with Waldron & Cassinelli (2007) for centralV
 X-rays best for measurements of v∞
High-Resolution X-rays from Hot Stars
Andy Pollock
XMM-Newton SOC
European Space Astronomy Centre
Villafranca del Castillo, Madrid, Spain
The problem with the X-ray lines of O stars
 Too symmetric (cf Owocki & Cohen 2001)
 Ingredients for a solution
 X-ray opacity
 Reduction by UV, EUV & X-rays (Waldron 1984 et seq)
 Porosity (Owocki & Cohen 2006)
 Vela X-1 test ?
 Location, location, location
 X(v(r)) = fX (v(r>R0)) (red half from behind the star)
 CIE He-like triplets (Cassinelli+ 2001 Leutenegger+ 2006)
Waldron+ (1998)
High-Resolution X-rays from Hot Stars
Cassinelli+
(2001)
Townsend
via Owocki & Cohen (2006)
Andy Pollock
XMM-Newton SOC
European Space Astronomy Centre
Villafranca del Castillo, Madrid, Spain
Some of the contenders
 Oskinova+ (2006)
 CIE He-like locations
 POWR opacities
 highly clumped cool wind
 1 clump per flow time
 Cohen & Leutenegger (2007)
 empirical X-ray opacity
 X-ray starting radius
 wind porosity parameter
 Pup
 Pollock 2007, A&A, 463, 1111
 abandon all this
High-Resolution X-rays from Hot Stars
Andy Pollock
XMM-Newton SOC
European Space Astronomy Centre
Villafranca del Castillo, Madrid, Spain
A new paradigm for single O stars
 All X-ray lines have the same velocity profile
 terminal velocity regime
 widths are from random not bulk velocities
 Plasma is not in equilibrium
 reconsider CIE He-like radii
 Plasma is collisionless (cf SNR shocks)
 relaxation times are long and energy exchange is slow
 no prompt hot electrons and no continuum
 ionization and excitation by means other than electron impact
 charge exchange
 proton excitation ? v∞  vBohr !
 rates ?
 B important
 Are shocks required at all ?
 Many outstanding questions
 origin of FeXVII 16.778 and exchange-term lines
 Why no RRCs ?
High-Resolution X-rays from Hot Stars
Andy Pollock
XMM-Newton SOC
European Space Astronomy Centre
Villafranca del Castillo, Madrid, Spain
High-velocity microphysics of charged particles
electron >< ion
ion >< ion
elastic collisions
inelastic collisions
Coulomb collisions
 ii  7 1021cm 2
 ei   ii me /mi
excitation
charge exchange
Spitzer (1956)
ionization

no neutral gas in hot-star winds
ii  excitation  ionization  charge exchange  10-17 – 10-15 cm2
High-Resolution X-rays from Hot Stars
Andy Pollock
XMM-Newton SOC
European Space Astronomy Centre
Villafranca del Castillo, Madrid, Spain
WR11 WC8+O at two binary phases
X()
Schild+ (2004)
X()
CVI
RRC
CV
RRC
Willis, Schild & Stevens, A&A, 298, 549, 1995
High-Resolution X-rays from Hot Stars
Andy Pollock
XMM-Newton SOC
European Space Astronomy Centre
Villafranca del Castillo, Madrid, Spain
WR48 WC5-6+OV+OI and a bright SNR
WR48 & SNR1ES0102-7219
OVIII
RRC
High-Resolution X-rays from Hot Stars
OVII
RRC
WR48
• PSPC constant over P=19d
• No photoionizing continuum
CVI
RRC
Andy Pollock
XMM-Newton SOC
European Space Astronomy Centre
Villafranca del Castillo, Madrid, Spain
X-rays from 1 Ori C (B=1.1kG, P=15.4d)
Gagné+ 2005
O4-5
WC7
 Wind dynamics dominated by B
 Lines from OVII to FeXXV hotter and narrower than other O stars
 “magnetically-channeled wind shock” MHD simulations work well
 models of  Sco (B=0.5kG, P=41d) coming soon
High-Resolution X-rays from Hot Stars
Andy Pollock
XMM-Newton SOC
European Space Astronomy Centre
Villafranca del Castillo, Madrid, Spain
X-rays from WR140 (P=7.94yr, D=14.1AU, e=0.88)
Pollock+ 2005
WR140 RXTE 2-10 keV (1-6Å)
WR in front
O4-5
WC7
©
©
http://lheawww.gsfc.nasa.gov/users/corcoran/wr140/wr140_rxte_lightcurves/Images/pcu2_l1_time.jpg
¡ CWB gas is not an ideal fluid !
 current hydrodynamic simulations are obsolete including mine
 there is no contact discontinuity
 B is important here too
High-Resolution X-rays from Hot Stars
Andy Pollock
XMM-Newton SOC
European Space Astronomy Centre
Villafranca del Castillo, Madrid, Spain
The best Wolf-Rayet binary X-ray spectrum
WR140 Chandra HETG just before the 2001 periastron
 vpshock models fit well
¿ …but what does it mean ?
 X-rays best for abundances
High-Resolution X-rays from Hot Stars
Andy Pollock
XMM-Newton SOC
European Space Astronomy Centre
Villafranca del Castillo, Madrid, Spain
Details of WR140’s HETG X-ray lines
¡ this plasma is not in equilibrium !
High-Resolution X-rays from Hot Stars
Andy Pollock
XMM-Newton SOC
• near periastron
• near apastron
European Space Astronomy Centre
Villafranca del Castillo, Madrid, Spain
X-rays from  Carinae (P=5.5yr, e~0.9)
Henley+ (2007)
• Equilibrium ionization ?
• He-like f/i ratio > low-density upper limit
• same as WR140
High-Resolution X-rays from Hot Stars
Andy Pollock
XMM-Newton SOC
European Space Astronomy Centre
Villafranca del Castillo, Madrid, Spain
Statistical asides
 Poisson statistics always apply
 P(n|) = e-n/n!
 0 is a perfectly good measurement
 P(0|) = e-
 log(likelihood) like XSPEC’s C-statistic is always valid
 C-statistic goodness-of-fit needs work for lots of  ~ 0
 Never rebin even low-resolution spectra
 Who rebins beautiful 0.5” resolution Chandra spatial images ?
 Plot in linear coordinates
High-Resolution X-rays from Hot Stars
Andy Pollock
XMM-Newton SOC
European Space Astronomy Centre
Villafranca del Castillo, Madrid, Spain
Are magnetic fields the key to hot-star X-rays ?
 1 Ori C when B is dynamically in charge
  Ori when it’s not
 Distant binaries like WR140 and WR25 generate their own B
 Observational work required
 1 O star for 1 HETG Ms to emulate Capella
 cf Leutenegger+ (2007) NVI and OVII resonance scattering in  Pup
 continuum level
 distinguish alternative models
 2009 January periastron passages of WR140 and  Carinae
 close binaries in general
 CHM rather than CWB
 Theoretical work required
 proton ionization rates
 charge exchange
 NEI models
High-Resolution X-rays from Hot Stars
Andy Pollock
XMM-Newton SOC
European Space Astronomy Centre
Villafranca del Castillo, Madrid, Spain