||Solving the Puzzle of the Massive Star System θ2 Orionis A
||464, Circumstellar Dynamics at High Resolution
||Petit, V.; Gagné, M.; Cohen, D. H.; Townsend, R. H. D.; Leutenegger, M. A.; Savoy, M. R.; Fehon, G.; Cartagena, C. A.
||The young O9.5 V spectroscopic binary θ2 Ori A shows moderately
hard X-ray emission and relatively narrow X-ray lines, suggesting that it may
be a Magnetically Confined Wind Shock (MCWS) source, similar to its more
massive analogue θ1 Ori C. X-ray flares occurring near periastron
led to the suggestion that the flares are produced via magnetic reconnection
as magnetospheres on both components of the θ2 Ori A binary interact
at closest approach.
We use a series of high-resolution spectropolarimetric observations of
θ2 Ori A to place an upper limit on the magnetic field strength of
135 G (95% credible region). Such a weak dipole field would not produce
magnetic confinement, or a large magnetosphere. A sub-pixel analysis of the
Chandra ACIS images of θ2 Ori A obtained during quiescence and
flaring show that the hard, flaring X-rays are offset from the soft, quiescent
emission by 0.4 arcsec. If the soft emission is associated with the A1/A2
spectroscopic binary, the offset and position angle of the hard, flaring
source place it at the location of the intermediate-mass A3 companion,
discovered via speckle interferometry. The spectropolarimetric and X-ray
results taken together point to the A3 companion, not the massive A1/A2
binary, as the source of hard, flaring X-ray emission.
We also discuss a similar analysis performed for the magnetic Bp star σ Ori E. We find a similar origin for its X-ray flaring.