Solving the long-standing issue of the evolutionary state of MWC 349A

CIDALE, L. S.; ARIAS, M. L.; KRAUS, M.; TORRES, A. F.

La Plata

Workshop; Workshop Observatorio Gemini en Argentina: Actualidad y Prospección; 2018

The star MWC 349A is one of the brightest radio stars on the sky. Its radio spectrum indicates an ionized wind expanding at 25-30 km/s and a mass-loss rate of 1d-5 solar masses per year. Radio continuum observations revealed that the wind has a bipolar shape, and spectroscopic and spectropolarimetric observations suggest the presence of an almost edge-on seen thick disk with both an ionized and a neutral component. The object is famous for its hydrogen recombination maser and laser lines from the far-infrared up to the millimeter range that emerge from the Keplerian disk and the rotating bipolar wind. CO band emission has been reported from this object, originating from the far inner rim of the molecular disk. The large infrared excess emission further implies a huge amount of dust within the disk. The presence of a thick dusty disk plus bipolar outflow are typical signs for a young, pre-main sequence nature of the object.However, the discovery of a huge bipolar infrared nebula associated with MWC 349A and spreading over about 5 pc proposes an evolved nature as either a B[e] supergiant or a Luminous Blue Variable. A way to disentangle between these contradictory evolutionary states is to search for tracers in the circumstellar material that give direct proof of the age of the star. One such tracer is the emission in 13CO, which directly relates to the 12C/13C ratio. Any enrichment of the circumstellar matter with 13C would be a direct proof of an evolved nature of MWC 349A. To search for 13CO, we obtained a K-band spectrum (R~5100) of MWC 349A using GNIRS. Careful analysis of this spectrum allows us to resolve the ambiguity and to assign MWC 349A once and for all a proper evolutionary state.