Solving the Puzzle of the Massive Star Systems θ2 Orionis A and σ Orionis E

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
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