MWC349A and B Are Not Gravitationally Bound: New Evidence

TL;DR

This study presents evidence that MWC349A and B are not gravitationally bound, suggesting MWC349A may be a young star near Cyg OB2, with MWC349B possibly being a runaway star from that region.

Contribution

It provides new high-resolution spectral data showing the stars are not gravitationally bound, challenging previous assumptions about MWC349A's evolutionary status.

Findings

Radial velocity difference of ~35 km/s between MWC349A and B.

High proper motion of MWC349B supports it being a runaway star.

MWC349A may be a young star near Cyg OB2, not an evolved massive star.

Abstract

The age and evolutionary status of MWC349A, the unique emission line star with maser and laser radiation in hydrogen recombination lines, remain unknown because the spectrum of the star is veiled by bright emission from the ionized disk and wind. The major argument for this massive ($>$10 M_sun) star being evolved is its association with a close-by (2.4 arcsec) companion, MWC349B, whose B0III spectrum implies an age of a few Myrs. However, newly obtained high-resolution spectra of MWC349B reveal a difference $\approx$ 35 km/s in the radial velocities of the two stars, which makes their being gravitationally bound highly improbable. An estimate of the relative proper motion of the two stars seems to confirm this conclusion. This reopens the previously suggested possibility that MWC349A is a young massive star in a region of active star formation close to the Cyg OB2 association. MWC349B, which moves with a speed $\geq$ 35 km/s relative to Cyg OB2, may be a runaway star from this association.