Are MWC349 A and B a Physical Binary?

The age and evolutionary status of the only known hydrogen recombination line maser and laser star MWC349A, "A", is unknown because its spectrum has no absorption features for classification. Star A has an optical B0III companion 2.4 arcsec away, MWC349B. Previous studies suggest A & B are either gravitationally bound, and therefore both a few Myr old, or not bound and A is possibly an observable 30 M_solar star in its pre-main sequence stage. We attempt to solve the controversy by measuring the difference of radial velocities between A and B using observations from the 1.5m Tillinghast telescope and the TRES spectrometer at the Whipple Observatory. With an assumed distance of 1.2 kpc and masses of ~30 M_solar, the radial velocities cannot differ by >3 km/s for the stars to be gravitationally bound. We find a radial velocity with respect to the local standard of rest of 42 ± 18 km/s for B, and compare it with the known radial velocity of 8 ± 2 km/s for A giving a difference of 34 ± 20 km/s - much greater than 3 km/s. We conclude that A and B are not gravitationally bound, although light contamination from star A in B's spectrum makes this result somewhat inconclusive. If confirmed, however, the known spectral type of B will not determine the age of star A and star A may be an observable 30 M_solar star in its pre-main sequence stage. We gratefully acknowledge support from Dave Latham, Jessica Mink and the TRES instrument team. This project was supported in part by the NSF REU grant AST-1358980 and by the Maria Mitchell Association.