The long period eccentric orbit of the particle accelerator HD167971 revealed by long baseline interferometry

M. De Becker (1), H. Sana (2), O. Absil (1), J.-B. Le Bouquin (3), R. Blomme (4)

1. University of Li├Ęge, Belgium
2. University of Amsterdam, Netherlands
3. UJF-Grenoble, France
4. Royal Observatory of Belgium, Belgium

Using optical long baseline interferometry, we resolved for the first time the two wide components of HD167971, a candidate hierarchical triple system known to efficiently accelerate particles. Our multi-epoch VLTI 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 three-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. HD167971 turns out to be an efficient O-type particle accelerator that constitutes a valuable target for future high angular resolution radio imaging using VLBI facilities.

Reference: MNRAS (in press)
Status: Manuscript has been accepted