Discovery of a parsec-scale bipolar nebula around MWC 349A

TL;DR

This paper reports the discovery of a large bipolar nebula around MWC 349A using infrared data, revealing its extended structure and proposing a stellar origin involving a hierarchical triple system and stellar evolution.

Contribution

It presents the first detection of a parsec-scale bipolar nebula around MWC 349A and suggests a new evolutionary scenario involving a hierarchical triple system.

Findings

Discovery of a 5 pc bipolar nebula around MWC 349A

Proposal that MWC 349A is an evolved massive star in a binary system

Evidence supporting a hierarchical triple system origin

Abstract

We report the discovery of a bipolar nebula around the peculiar emission-line star MWC 349A using archival Spitzer Space Telescope 24 um data. The nebula extends over several arcminutes (up to 5 pc) and has the same orientation and geometry as the well-known subarcsecond-scale (~400 times smaller) bipolar radio nebula associated with this star. We discuss the physical relationship between MWC 349A and the nearby B0 III star MWC 349B and propose that both stars were members of a hierarchical triple system, which was ejected from the core of the Cyg OB2 association several Myr ago and recently was dissolved into a binary system (now MWC 349A) and a single unbound star (MWC 349B). Our proposal implies that MWC 349A is an evolved massive star (likely a luminous blue variable) in a binary system with a low-mass star. A possible origin of the bipolar nebula around MWC 349A is discussed.