Solving the Puzzle of the Massive Star System Theta 2 Orionis A

TL;DR

This study investigates the origin of X-ray emissions in the Theta 2 Orionis A system, concluding that the intermediate-mass A3 companion, not the primary binary, is responsible for the flaring activity, challenging previous assumptions.

Contribution

The paper provides the first combined spectropolarimetric and high-resolution X-ray analysis to identify the true source of X-ray flaring in Theta 2 Ori A, emphasizing the role of the A3 companion.

Findings

Weak magnetic field in Theta 2 Ori A's primary binary rules out magnetic confinement.

X-ray flares originate from the A3 companion, not the primary binary.

Similar X-ray flaring mechanisms are observed in the magnetic Bp star Sigma Ori E.

Abstract

The young O9.5 V spectroscopic binary Theta 2 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 Theta 1 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 Theta 2 Ori A binary interact at closest approach. We use a series of high-resolution spectropolarimetric observations of Theta 2 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 Theta 2 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 Sigma Ori E. We find a similar origin for its X-ray flaring.