X-ray Variability in the Young Massive Triple θ2 Ori A
Abstract
Massive stars rarely show intrinsic X-ray variability. The only O-stars credited to be intrinsically variable are theta1 Ori C due to effects from magnetic confinement of its wind, and theta2 Ori A suspected of similar activity. In the latter case early Chandra observations have shown rapid variability on time scales of hours. We determined X-ray fluxes from all observations with Chandra and find that the star shows very strong variability over the last 5 years in addition to short term varibility. There indications that this variability is connnected to the 21 day orbital period of the massive spectrocopic binary causing eruptive outbursts near periastron. A second large outburst of the X-ray source in November 2004 was observed with the high resolution transmission grating spectrometer onboard Chandra and we compare the emissivity and line properties in states of low and high flux. 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 ×1037 ergs. Both flux states reveal high X-ray emissivities with temperatures well above 25 MK, during outbursts over 100 MK. The line diagnostics show that under the assumption that the He-like ions are photoexcited the line emitting regions in the low states are very close to the O-star's photosphere, whereas the high states indicate somewhat larger separation. We discuss the results in the context of stellar flares, magnetic reconnection, and binary interactions. We argue that the high X-ray states are possibly the result of reconnection events from magnetic interactions of the primary and secondary star of the spectroscopic binary. Effects from wind collisions seem unlikely for this system. The low state emissivity and R-ratios strengthen the predicament that X-ray emission is enhanced by magnetic confinement of the primary wind.
- Publication:
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American Astronomical Society Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AAS...20913305S