An Apparent Precessing Helical Outflow from a Massive Evolved Star: Evidence for Binary Interaction?

Massive, evolved stars play a crucial role in the metal-enrichment, dust budget, and energetics of the interstellar medium; however, the details of their evolution are uncertain because of their rarity and short lifetimes before exploding as supernovae. Discrepancies between theoretical predictions from single-star evolutionary models and observations of massive stars have evoked a shifting paradigm that implicates the importance of binary interaction. We present mid- to far-infrared observations from the Stratospheric Observatory for Infrared Astronomy (SOFIA) of a conical “helix” of warm dust (∼180 K) that appears to extend from the Wolf-Rayet star WR102c. Our interpretation of the helix is a precessing, collimated outflow that emerged from WR102c during a previous evolutionary phase as a rapidly rotating luminous blue variable. We attribute the precession of WR102c to gravitational interactions with an unseen compact binary companion whose orbital period can be constrained to 800 d < P < 1480 d from the inferred precession period, τ _p ~1.4 × 10 ⁴ yr, and limits imposed on the stellar and orbital parameters of the system. Our results concur with the range of orbital periods (P < 1500 d) where spin-up via mass exchange is expected to occur for massive binary systems.