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X-rays from single O-stars

X-rays from single O-stars. Guedel M. & Naze Y. Astronomy Astrophysics Rev (2009) 17:309 Oct. 17, 2011. Outlines. discovery of X-rays from O-stars; properties model prediction results from high-resolution spectra new paradigm?. X-rays from hot stars: discovery.

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X-rays from single O-stars

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  1. X-rays from single O-stars Guedel M. & Naze Y. Astronomy Astrophysics Rev (2009) 17:309 Oct. 17, 2011

  2. Outlines • discovery of X-rays from O-stars; • properties • model prediction • results from high-resolution spectra • new paradigm?

  3. X-rays from hot stars: discovery • Einstein observation on Cyg OB2 (Harnden et al. 1979) • Confirmed the prediction by Cassinelli & Olson (1979)

  4. Properties: nature of the emission • Mainly thermal: • discrete metal lines superimposed on a • (weak) continuum bresstrahlung emission; • kT: 0.3 & 0.7-1.0 keV From Naze and Rauw 2008

  5. Property: LX/Lbol relation • Generally, (see Owocki et al. 2011) • Observationally, • (Berghoefer et al. 1997, RASS); • (Sana et al. 2006, XMM on NGC 6231); • (Antokhin et al. 2008, XMM on Carina OB1) • Breaking down at lower luminosities (Cassinelli et al. 1994, ROSAT on near B-stars)

  6. Model: origin of X-rays • Why not corona? • Absorption is too weak (Cassinelli & Swank 1983); • No coronal line [Fe XIV] λ5303 (Nordsieck et al. 1981); • Line profiles from “superionized” species were incompatible (Macfarlane et al. 1993, OIV P Cygni profile of ζ Pup). • Wind-shock scenario is more favored (Lucy & White 1980; Feldmeier et al. 1997).

  7. Winds of hot stars • Line-driven: (Vink 2005, Puls et al. 2008); • Typical mass-loss rate: ; • Terminal velocity: ~2,000 km/s; • Main contributors to the mechanical input, chemical enrichment; modify the environment; • Porosity?

  8. Model: expectation

  9. Results from high-res. spectra

  10. ζ Ori A (O9.7Ib): • broad (HWHM=850 km/s, Walborn & Cassinelli 2001); • slight asymmetric and blueshifted (Cohen et al. 2006); • need mass-loss rate decreased by 1o. • δ Ori A (O9.5II+B0.5III, Miller et al. 2002): • broad (FWHM~430 km/s), unshifted; • R0~2R* • binarity does not affect the X-rays. • ζ Oph (O9.5Ve, Waldron 2005): • broad (FWHM~400 km/s, slightly blueshifted; • R0=(1.9-9.0) R* (Oskinova et al. 2006).

  11. New paradigm: clumping • proof: • line-profile variability; • incompatible P Cygni profiles with canonical model. • micro- vs. macro- (porosity): • size of clumping comparing to the mean free path of photon: same size or much larger; • opacity of clumping: thin or thick; • effect: affect optical-thin lines (e.g., Hα) or optical-thick lines (e.g., PV resonance doublet); • Micro-clumping scenario will reduce the mass-loss rate.

  12. Effect on X-rays

  13. Thanks!

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