The ${}^{13}$Carbon footprint of B[e] supergiants

Abstract

We report on the first detection of ${}^{13}$C enhancement in two B[e] supergiants in the Large Magellanic Cloud. Stellar evolution models predict the surface abundance in ${}^{13}$C 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 ${}^{13}$C via the molecular emission in ${}^{13}$CO 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 ${}^{13}$CO 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 ${}^{13}$CO band emission, whose strength implies a strong enhancement of ${}^{13}$C, 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.

5 pages, 4 figures, accepted for publication in MNRAS Letters

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