Bonn 2020 – scientific programme

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EP: Fachverband Extraterrestrische Physik

EP 12: Astrophysics II

EP 12.2: Talk

Friday, April 3, 2020, 09:30–09:45, H-HS VIII

Evidence of an evolved nature of MWC 349A — •Michaela Kraus¹, Maria Laura Arias², Lydia Cidale², and Andrea Torres² — ¹Astronomical Institute, Czech Academy of Sciences, Ondrejov, Czech Republic — ²Institute of Astrophysics, CONICET-UNLP, La Plata, Argentina

The Galactic emission-line object MWC 349A is one of the brightest radio stars in the sky. The central object is embedded in an almost edge-on oriented Keplerian rotating thick disk that seems to drive a rotating bipolar wind. The dense disk is also the site of the hot molecular emission such as the CO bands with its prominent band heads in the near-infrared spectral range. Despite numerous studies, the nature of MWC 349A is still controversial with classifications ranging from a pre-main sequence object to an evolved supergiant. To study the molecular disk of MWC 349A, and in particular to search for the isotope 13CO, we collected new high-resolution near-infrared spectra using the GNIRS spectrograph at Gemini-North. The amount of 13CO, obtained from the 12CO/13CO ratio, is recognized as an excellent tool to discriminate between pre-main sequence and evolved massive stars. We detect CO band emission with considerably lower intensity and CO gas temperature compared to previous observations. Moreover, from detailed modeling of the mission spectrum, we derive an isotope ratio of 12CO/13CO of 4. Based on this significant enrichment of the circumstellar environment in 13CO we conclude that MWC 349A belongs to the group of B[e] supergiants, and we discuss possible reasons for the drop in CO intensity.