Journal Article

The long-period eccentric orbit of the particle accelerator HD 167971 revealed by long baseline interferometry*

M. De Becker, H. Sana, O. Absil, J.-B. Le Bouquin and R. Blomme

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 423, issue 3, pages 2711-2717
Published in print July 2012 | ISSN: 0035-8711
Published online June 2012 | e-ISSN: 1365-2966 | DOI:
The long-period eccentric orbit of the particle accelerator HD 167971 revealed by long baseline interferometry*

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Using optical long baseline interferometry, we resolved for the first time the two wide components of HD 167971, a candidate hierarchical triple system known to efficiently accelerate particles. Our multi-epoch Very Large Telescope Interferometer observations provide direct evidence for a gravitational link between the O8 supergiant and the close eclipsing O + O binary. The separation varies from 8 to 15 mas over the 3-year baseline of our observations, suggesting that the components evolve on a wide and very eccentric orbit (most probably e > 0.5). These results provide evidence that the wide orbit revealed by our study is not coplanar with the orbit of the inner eclipsing binary. From our measurements of the near-infrared luminosity ratio, we constrain the spectral classification of the components in the close binary to be O6–O7, and confirm that these stars are likely main-sequence objects. Our results are discussed in the context of the bright non-thermal radio emission already reported for this system, and we provide arguments in favour of a maximum radio emission coincident with periastron passage. HD 167971 turns out to be an efficient O-type particle accelerator that constitutes a valuable target for future high angular resolution radio imaging using Very Long Baseline Interferometry facilities.

Keywords: radiation mechanisms: non-thermal; techniques: interferometric; binaries: general; stars: early-type; stars: individual: HD 167971

Journal Article.  5614 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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