The 13Carbon footprint of B[e] supergiants

A. Liermann1, 2, M. Kraus3, O. Schnurr4, 5, M. Borges Fernandes6

1Universität Potsdam, Institut für Physik und Astronomie, Karl-Liebknecht-Str. 24-25, 14476 Potsdam, Germany
2Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
3Astronomický ústav, Akademie vĕd České republiky, Fričova 298, 251 65 Ondřejov, Czech Republic
4University of Sheffield, Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH, UK
5Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
6Observatório Nacional, Rua General José Cristino 77, 20921-400 Sao Cristovão, Rio de Janeiro, Brazil

We report on the first detection of 13C enhancement in two B[e] supergiants in the Large Magellanic Cloud. Stellar evolution models predict the surface abundance in 13C to strongly increase during main-sequence and post-main sequence evolution of massive stars. However, direct identification of chemically processed material on the surface of B[e] supergiants is hampered by their dense, disk-forming winds, hiding the stars. Recent theoretical computations predict the detectability of enhanced 13C via the molecular emission in 13CO arising in the circumstellar disks of B[e] supergiants. To test this potential method and to unambiguously identify a post-main sequence B[e]SG by its 13CO emission, we have obtained high-quality K-band spectra of two known B[e] supergiants in the Large Magellanic Cloud, using the Very Large Telescope's Spectrograph for INtegral Field Observation in the Near-Infrared (VLT/SINFONI). Both stars clearly show the 13CO band emission, whose strength implies a strong enhancement of 13C, in agreement with theoretical predictions. This first ever direct confirmation of the evolved nature of B[e] supergiants thus paves the way to the first identification of a Galactic B[e] supergiant.

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