GRAVITY spectro-interferometric study of the massive multiple stellar system HD 93 206 A

Sanchez-Bermudez, J.; Alberdi, A.; Barba, R.; Bestenlehner, J. M.; Cantalloube, F.; Brandner, W.; Henning, Th.; Hummel, C. A.; Maiz Apellaniz, J.; Pott, J.-U.; Schoedel, R.; van Boekel, R.
The Astrophysical Journal, Volume 845, Issue 1, article id. 57, 13 pp. (2017).


Characterization of the dynamics of massive star systems and the astrophysical properties of the interacting components are a prerequisite for understanding their formation and evolution. Optical interferometry at milliarcsecond resolution is a key observing technique for resolving high-mass multiple compact systems. Here, we report on Very Large Telescope Interferometer/GRAVITY, Magellan/Folded-port InfraRed Echellette, and MPG2.2 m/FEROS observations of the late-O/early-B type system HD 93206 A, which is a member of the massive cluster Collinder 228 in the Carina nebula complex. With a total mass of about 90 {M}ȯ , it is one of the most compact massive quadruple systems known. In addition to measuring the separation and position angle of the outer binary Aa–Ac, we observe Brγ and He i variability in phase with the orbital motion of the two inner binaries. From the differential phase ({{{Δ }}}φ ) analysis, we conclude that the Brγ emission arises from the interaction regions within the components of the individual binaries, which is consistent with previous models for the X-ray emission of the system based on wind–wind interaction. With an average 3σ deviation of {{{Δ }}}φ ∼ 15^\circ , we establish an upper limit of p ∼ 0.157 mas (0.35 au) for the size of the Brγ line-emitting region. Future interferometric observations with GRAVITY using the 8 m Unit Telescopes will allow us to constrain the line-emitting regions down to angular sizes of 20 μas (0.05 au at the distance of the Carina nebula).