Abstract by Marc Gagné et al.
In the standard picture of radiatively driven winds, X-rays from single, massive stars are produced in shocks generated throughout the wind. While colliding wind binaries like η Carinae and magnetic O stars like θ1 Ori C show hard, time-variable X-ray emission, most OB stars produce relatively soft, steady X-ray emission (kT ≈ 0.5 keV). Two massive stars however have exhibited unusual X-ray flares: the magnetic B2 Vp star σ Ori E (Sanz-Forcada et al. 2004) and the spectroscopic binary O9.5 V system θ2 Ori A (Schulz et al. 2006). ud-Doula et al. (2006) suggested that the events on σ Ori E were evidence of centrifugal breakout of magnetically confined wind shocks, while Schulz et al. (2006) suggested that the flares on θ2 Ori A might be caused by magnetospheric interactions between the A1/A2 components near periastron.
In this talk we present new spectropolarimetric observations of θ2 Ori A that show a broad He I absorption line from the A2 secondary, and no evidence of strong magnetic fields in the Stokes-V profiles. Via a careful sub-pixel reconstruction of the Chandra X-ray images we also show that the hard, time variable X-ray emission is offset from the soft, steady X-ray source by 0.3”. The X-ray flare position is coincident with the position of the infrared A3 companion reported by Preibisch et al. (1999). Similarly, our sub-pixel reconstruction of the Chandra High-Resolution Camera image of σ Ori E shows that the flaring emission is offset by 0.4” from the magnetic primary, coincident with an infrared speckle companion discovered by Buoy et al. (2009). Thus, intermediate-mass young stellar objects produce the hard X-ray flares in both systems.
Background Papers
“The magnetic field of Sigma Orionis E”
Landstreet, J. D. & Borra, E. F.
“Multiplicity of the massive stars in the Orion Nebula cluster”
Preibisch, T. et al.
“XMM-Newton observations of the σ Ori cluster. I. The complex RGS spectrum of the hot star σ Ori AB”
Sanz-Forcada et al.
“X-Ray Variability in the Young Massive Triple θ2 Orionis A”
Schulz, N., et al.
“Centrifugal Breakout of Magnetically Confined Line-driven Stellar Winds”
ud-Doula, A., Townsend, R. H. D., & Owocki, S. P.
“A deep look into the cores of young clusters. I. σ Orionis”
Bouy, H. et al.
Talk Slides
pdf
Friday, February 17, 2012
Friday, February 3, 2012
Mass loss from the structured winds of hot, massive stars
Abstract by Jon Sundqvist
It is observationally as well as theoretically well-established that
the winds of hot, massive stars are highly structured on a broad range
of spatial scales. This talk first discusses consequences of the
small-scale structures associated with the strong instability inherent
to the line-driving of these winds. We demonstrate the importance of a
proper treatment of such wind clumping (including effects of optically
thick clumps and a non-monotonic velocity field) to accurately
interpret wind diagnostics and obtain reliable estimates of mass-loss
rates. But a growing subset of massive stars has also been found to
possess strong surface magnetic fields, which may channel the star's
wind outflow and so induce also large-scale structures and cyclic
behaviour of spectral diagnostics. The talk concludes by presenting
our recent result showing that multi-dimensional
magneto-hydrodynamical wind simulations together with detailed
radiative-transfer modeling remarkably well reproduce the periodic
Balmer emission observed in slowly rotating magnetic O stars.
Background Papers
"The nature and consequences of clumping in hot,
massive star winds"
Sundvist, Owocki, & Puls, 2011arXiv1110.0485S
It is observationally as well as theoretically well-established that
the winds of hot, massive stars are highly structured on a broad range
of spatial scales. This talk first discusses consequences of the
small-scale structures associated with the strong instability inherent
to the line-driving of these winds. We demonstrate the importance of a
proper treatment of such wind clumping (including effects of optically
thick clumps and a non-monotonic velocity field) to accurately
interpret wind diagnostics and obtain reliable estimates of mass-loss
rates. But a growing subset of massive stars has also been found to
possess strong surface magnetic fields, which may channel the star's
wind outflow and so induce also large-scale structures and cyclic
behaviour of spectral diagnostics. The talk concludes by presenting
our recent result showing that multi-dimensional
magneto-hydrodynamical wind simulations together with detailed
radiative-transfer modeling remarkably well reproduce the periodic
Balmer emission observed in slowly rotating magnetic O stars.
Background Papers
"The nature and consequences of clumping in hot,
massive star winds"
Sundvist, Owocki, & Puls, 2011arXiv1110.0485S
Iron-line diagnostics in the extreme colliding-wind binary Eta Carinae
Abstract by Jean-Christophe Leyder
Eta Carinae, one of the most peculiar objects in our Galaxy, was the second brightest object in the sky during its eruption in 1843. The large quantities of matter that were ejected at that time are now forming an extended nebula, while Eta Car is still ejecting matter through energetic stellar winds. Eta Car is a colliding-wind binary system: the dense stellar wind coming from the massive luminous blue variable primary star collides with the higher-velocity, lower-density wind from the hotter and luminous (and otherwise unseen) companion star in a highly eccentric orbit. Monitoring observations in the radio, UV, optical, and X-ray domains all indicate an orbital period of 5.5 years.
X-ray observations of a colliding-wind binary system such as Eta Carinae provide numerous clues as to the shock physics and mechanisms responsible for particle acceleration and emission in the hydrodynamical shocks that form between the stellar winds. Furthermore, Eta Carinae's long period and high eccentricity provides varying physical conditions, and allow to probe a large parameter space of densities and wind speeds, especially when observing periastron passages where strong variations occur over a short timescale.
In this talk, I will present a set of 23 high-resolution X-ray spectra of Eta Carinae obtained by the Chandra satellite, with a particularly detailed coverage around the X-ray minima of 2003.5 and 2009. I will focus on the variations and peculiarities observed in the Fe K line region. First noticed by Hamaguchi et al. 2007, the existence of a variable “red wing” in the profile of the Fe XXV triplet is puzzling. I will discuss possible hypothesis for the unexpected presence of such a "red wing" : the presence of an extremely bright, relatively cool, and heavily absorbed equilibrium plasma; emission due to unshocked photoionized wind material; or the possibility that a fraction of the thermal plasma is not in ionization equilibrium.
Background Papers
"X-Ray Spectral Variation of Eta Carinae through the 2003 X-Ray Minimum"
Hamaguchi K. et al. 2007
"Recent X-ray Variability of Eta Carinae: The Quick Road to Recovery"
Corcoran M.F. et al. 2010
"Chandra X-Ray Grating Spectrometry of Eta Carinae near X-Ray Minimum. I. Variability of the Sulfur and Silicon Emission Lines"
Henley D.B. et al. 2008
"Bulk Velocities, Chemical Composition, and Ionization Structure of the X-Ray Shocks in WR 140 near Periastron as Revealed by the Chandra Gratings"
Pollock A.M.T. et al. 2005
Eta Carinae, one of the most peculiar objects in our Galaxy, was the second brightest object in the sky during its eruption in 1843. The large quantities of matter that were ejected at that time are now forming an extended nebula, while Eta Car is still ejecting matter through energetic stellar winds. Eta Car is a colliding-wind binary system: the dense stellar wind coming from the massive luminous blue variable primary star collides with the higher-velocity, lower-density wind from the hotter and luminous (and otherwise unseen) companion star in a highly eccentric orbit. Monitoring observations in the radio, UV, optical, and X-ray domains all indicate an orbital period of 5.5 years.
X-ray observations of a colliding-wind binary system such as Eta Carinae provide numerous clues as to the shock physics and mechanisms responsible for particle acceleration and emission in the hydrodynamical shocks that form between the stellar winds. Furthermore, Eta Carinae's long period and high eccentricity provides varying physical conditions, and allow to probe a large parameter space of densities and wind speeds, especially when observing periastron passages where strong variations occur over a short timescale.
In this talk, I will present a set of 23 high-resolution X-ray spectra of Eta Carinae obtained by the Chandra satellite, with a particularly detailed coverage around the X-ray minima of 2003.5 and 2009. I will focus on the variations and peculiarities observed in the Fe K line region. First noticed by Hamaguchi et al. 2007, the existence of a variable “red wing” in the profile of the Fe XXV triplet is puzzling. I will discuss possible hypothesis for the unexpected presence of such a "red wing" : the presence of an extremely bright, relatively cool, and heavily absorbed equilibrium plasma; emission due to unshocked photoionized wind material; or the possibility that a fraction of the thermal plasma is not in ionization equilibrium.
Background Papers
"X-Ray Spectral Variation of Eta Carinae through the 2003 X-Ray Minimum"
Hamaguchi K. et al. 2007
"Recent X-ray Variability of Eta Carinae: The Quick Road to Recovery"
Corcoran M.F. et al. 2010
"Chandra X-Ray Grating Spectrometry of Eta Carinae near X-Ray Minimum. I. Variability of the Sulfur and Silicon Emission Lines"
Henley D.B. et al. 2008
"Bulk Velocities, Chemical Composition, and Ionization Structure of the X-Ray Shocks in WR 140 near Periastron as Revealed by the Chandra Gratings"
Pollock A.M.T. et al. 2005
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