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

TL;DR

This study presents infrared observations of a precessing, helical dust outflow from the Wolf-Rayet star WR102c, providing evidence for binary interaction influencing massive star evolution through gravitational effects.

Contribution

It offers the first infrared evidence of a precessing outflow from WR102c, linking it to binary interaction and constraining the orbital period of the unseen companion.

Findings

Infrared helix suggests precessing outflow from WR102c.

Precession period constrains binary orbital period between 800 and 1400 days.

Results support binary interaction as key in massive star evolution.

Abstract

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 ($\sim180$ 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 $800\,\mathrm{d}<P<1400$ d from the inferred precession period, $\tau_p\sim1.4\times10^4$ yr, and limits imposed on the stellar and orbital parameters of the system. Our results concur with the range of orbital periods ($P\lesssim1500$ d) where spin-up via mass exchange is expected to occur for massive binary systems.