00 ShockingShocking TruthTruth aboutabout MassiveMassive StarsStars Lidia Oskinova Wolf-Rainer Hamann & Achim Feldmeier Potsdam University, Germany
ACIS Raw Detector Image of O-type supergiant ζ Puppis, CXO archive
Chandra's First Decade of Discovery 22 - 25 September 2009, Boston, Massachusetts, USA Massive Stars and Stellar Winds
Initial mass M∗ > 15M⊙
Main Sequence: OB-type
Fast evolution (~Myr) trace star formation
Hot. Teff > 10 000 K → high surface brightness
Photon momentum → acceleration of matter
Radiative acceleration larger than gravitation → supersonic STELLAR WIND nasaimages.org 03 OB stars are X-ray active (Einstein observatory 1978) Hot stars: radiatively driven stellar winds Supersonic stellar winds are intrinsically unstable ShocksShocks HeatingHeating X-RaysX-Rays
Shocks also result from: Collision of streams Collision of winds in magnetically confined wind in binaries 04 X-Ray Spectroscopy of Massive Stars ζ Ori Prediction of hydrodynamic models
NASA/EIT/W.Waldron, J.Cassinelli Models predict:
X-ray emitting plasma (TX = 1...10 MK) permeated with warm (T = 10 kK) absorbing wind X-rays originate at few R * from the core X-ray spectroscopy is needed! Distance [R ] Feldmeier et al. 1997 * Photo: G. Emerson, E.E. Barnard Observatory 05
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O-type stars 07 SXV SiXIV SiXIII MgXII MgXI NeX NeX NeIX FeXVIII FeXVII OVIII FeXVII FeXVII OVIII OVII NVII
0.2 ζ Pup O4I 0.1
0.0 ζ Ori 0.1 O9.7I o
0.0 0.03 ξ Per 0.02 O7.5III 0.01 0.00 0.10 ζ Oph
normalized counts/sec/A O9V 0.05
0.00 4 6 8 10 12 14 16 18 20 22 24 26 o Wavelength (A) Oskinova etal. 2007 08 Analyses of the HETGS spectra v = 0.03 ∞ 2450km/s ξ Per
Temperature ) o O7.5III Range from 2 MK to 10 MK 0.02 Emission line profiles Broad; width scales with wind speed 0.01
Line formation: deep in the wind Flux (Counts/sec/A
Similar accross the spectrum 0.00 0.12 v = Clumped wind treatment is needed ∞ 1550km/s ζ Oph 0.10 )
o O9V FIR line ratios 0.08 Formed close to the photosphere 0.06 Temperature decreases outward 0.04
Abundances Flux (Counts/sec/A0.02 Agree with wind abundances 0.00 Wojdowski & Schulz (2005), Oskinova etal (2006), 12.0 12.1 12.2 o Waldron & Cassinelly (2007), Zhekov & Palla (2007), etc. Wavelength (A) 09 Wind-shock Theory has Predictive Power
1.5 P V 3p 2 P - 3s 2 S UV and X-ray spectra microclumping micro- & macroclumping PV resonance doublet
1.0 Mass-loss rates!
Rel. Flux X-ray line profiles 0.5 X-ray spectra 0.0 1100 1110 1120 1130 1140 o λ / A Oskinova et al. 2007
0.20 ζ clumped wind Pup 8 DEM distribution same MÇ
10 )
o NeX 0.15 0.2 −4 107 −8 0.10 [K] T 6 0.1
10 −12Normalized Flux 0.05 Flux (Counts/sec/A smooth 5 10 wind 0.00 0 5 10 15 20 25 30 0.0 12.0 12.1 12.2 −1.0 −0.5 0.0 0.5 1.0 o x = r/R∗ Normalized Frequency Wavelength (A) Krticka et al. 2009 Oskinova et al. 10
B- 11 Chandra observations of α Cru
α Cru NeIX FeXVIII FeXVII OVIII FeXVII FeXVII OVIII OVII
X-ray brightest massive star on sky B0.5IV+BV at d=98 pc 13 14 15 16 17 18 19 20 21 22 23 24 Companion B1V α Cru NVII NVII CVI Soft spectrum TX =1..3 MK Normalized counts
23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 SiXI MgX SiXI FeXVII SiX FeXVI SiX FeXVI
37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 Oskinova et al. in prep. o Wavelength A 12 Stationary plasma in B-stars Wind speed is 1500 km/s But lines are narrow Comparable to instrumental profile! He−like ions: f/i line ratio probes distance to stellar photosphere
OVII α Cru Capella X−ray plasma in B−stars Close to the photosphere Stationary
Flux (Counts/sec/Angstrom) λ λ λ Different from shocks R I F in O−type winds
0.0 Pulsations? Coronae? 21.5 21.6 21.7 21.8 21.9 22.0 22.1 22.2 12a The evolution of (very) massive stars Mass removal by wind drives Teff / kK the evolution 100 50 20 10 5 7 OB (short LBV) WR Winds are getting dense and more enriched 6 WR OB LBV Wolf−Rayet (WR) stars L → → → / 40 M WN WC WO SN L log 5
ZAMS
4 5 4
log Teff / K
Credit: NASA/CXC/SAO/F.Seward et al WR124 13 WN8−type Observed serendipitously by Chandra WN8 stars are X−ray quiet
Wolf-Rayet type stars
Image courtesy of D.Ducros and ESA 14 X-ray view on Wolf-Rayet Stars Not all WN−type stars emit X−rays. Lack of X−rays cannot be attributed only to the wind opacity (Oskinova et al. ’06)
X−ray spectra of single WN stars are harder than spectra of O−stars (Ignace et al. 2003)
Single WC stars are X−ray quiet (Oskinova et al. 2003)
X−ray bright WR stars are binaries (Oskinova & Hamann 2008)
ζ Pup (O−type) WR 1 (WN) WR 114 (WC) 16 Closest WO-type Star WR142 in the Star Cluster Berkeley 87 Combined Spitzer (red+green) and EPIC (blue) image of the SFR ON 2
Only three WO stars are known in the MW
WO is the latest possible evolutionary stage of massive star
Core−collapse within 10 000 yr
Strongly influence their WR 142 environment
Oskinova et al. in prep. 17 Glimpse at the pre core-collapse star
-12
] 3
-1 -13 o 9.54 A 8.89 2 -2 -14 8.60 Rel. Flux cm 7.63 1 7.23 He II 5 - 4 -1 7.10 -15 0 6.69 10000 10500 o [erg s λ
λ / A -16
log F 5.35 -17
3.5 4.0 4.5 5.0 5.5 o Oskinova et al. 2009 log λ / A
Requires state−of−the art non−LTE models to fit observed optical and UV spectra. Such as PoWR code (Hamann et al. 2006) T =160 kK, R =0.5R , wind speed v=6000 km/s * * Our analysis indicates that star may be a FAST
ROTATOR Vrot sin i =4000 km/s. Current mass ~10 M 18 Discovery of X-ray emission from a WO-type star Strong enhancement by CO winds should be very * opaque for the X−rays X-rays are too hard to be explained by wind shocks * Hint on the presence of magnetic field B(r=2R ) > 7 kG * * Chandra detects hard X−rays from another compact fast * rotator WR2 (WN2)
0.00300
0.00250
0.00200
0.00150
0.00100
WR142 0.00050
1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 Oskinova et al. (2009) keV Mystery of X-rays from WR stars: Connection With Collapsars (?)
’’A very energetic explosion of a massive star is likely to create a ... fireball.... the inner core of a massive, rapidly rotating star collapses into a ~10 M Kerr black hole ... A superstrong ~1015 G magnetic field is needed to make the object ... a microquasar. Such events must be vary rare...to account for the ... GRBs’’ Do we indeed observe in our Galaxy massive, magnetic, rapidly rotating stars on latest stages of their evolution ? 20 Shocking truth? O−stars: X−rays are generated by wind shocks
B−stars: not clear: magnetic fields, pulsation, winds.
WR−stars: no hi−res spectrum exists! Magnetic field, rotation.
X−rays are sensitive probe of stellar winds Generation of X−rays in stellar winds is important physical problem
X−rays provide insights in stellar Chandra structure and evolution