X‐Ray Variability in the Young Massive Tripleθ²Orionis A

Abstract

Massive stars rarely show intrinsic X-ray variability. One exception is 2 Ori A, which has shown strong variability over the last 5 years. We observed a large outburst of the X-ray source with the High Energy Transmission Grating Spectrometer on board Chandra and compare the emissivity and line properties in states of low and high flux. The low state indicates temperatures well above 25 MK. In the high state we find high emissivities in the range from 3 to over 100 MK. The outburst event in stellar terms is one of the most powerful ever observed and the most energetic one in the ONC, with a lower total energy limit of 1:5 ; 10 37 ergs. The line diagnostics indicate that the line-emitting regions in the low states are as close as within 1Y2 stellar radii from the O star's photosphere, whereas the hard states suggest a distance of 3Y5 stellar radii. We discuss the results in the context of stellar flares, magnetic confinement, and binary interactions. By matching the dates of all observations with the orbital phases of the spectroscopy binary orbit, we find that outbursts occur very close to the periastron passage of the stars. We argue that the high X-ray states are possibly the result of reconnection events from magnetic interactions of the primary and secondary stars of the spectroscopic binary. Effects from wind collisions seem unlikely for this system. The line properties in the low state seem consistent with some form of magnetic confinement. We also detect Fe fluorescence indicative of the existence of substantial amounts of neutral Fe in the vicinity of the X-ray emission.

An X-ray survey of low-mass stars in Trumpler 16 with Chandra

“…appropiate, the magnetic reconnection from an unknown low-mass tertiary companion 23 cannot be ruled out. 23 Variability like HD 93205's has been seen also on theta 2 Ori-A and has been interpreted by Schulz et al (2006) as evidence of binaryinduced reconnection. However, image reconstruction shows that hard,…”

X-Ray Emission From Young Stars in the Massive Star-Forming Region Iras 20126+4104

“…Several models have been proposed to explain X-ray emission from early-type stars: shocks in line-driven winds in the outer atmosphere of the star (e.g., Lucy & White 1980), magnetically confined stellar winds (Gagné et al 2005), collisions of strong winds in close binary systems (e.g., Pittard & Parkin 2010), and binary-induced magnetic reconnection events (Schulz et al 2008). For massive stars in very early evolutionary states we also need to consider X-ray emission from accretion events (e.g., Günther et al 2007), as well as interaction of outflows/jets with the surrounding medium (e.g., Güdel et al 2005;Pravdo et al 2004).…”

Testing magnetically confined wind shock models for β Cephei using XMM-Newton and Chandra phase-resolved X-ray observations

“…Narrow lines imply a low-velocity plasma that has been interpreted as a confined plasma, likely requiring magnetic fields (e.g. Schulz et al 2003;Schulz et al 2006, and reference therein). Alternative scenarios, which do not require magnetic confinement for the X-ray emission from early-type stars showing narrow lines, have also been proposed Leutenegger et al 2006).…”