MWC 349A and B Are Not Gravitationally Bound: New Evidence

The age and evolutionary status of MWC 349A, 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⊙) star being evolved is its association with a close-by (2.4 arcsec) companion, MWC 349B, whose B0III spectrum implies an age of a few million years. However, newly obtained high-resolution spectra of MWC 349B reveal a difference of ≈35 km s−1 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 MWC 349A is a young massive star in a region of active star formation close to Cyg OB2 association. MWC 349B, which moves with a speed ≥35 km s−1 relative to Cyg OB2, may be a runaway star from this association.