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

A. Liermann (1,2), M. Kraus (3), O. Schnurr (4,5), M. Borges Fernandes (6)

1 - Universit"at Potsdam, Potsdam, Germany
2 - Max-Planck-Institut f"ur Radioastronomie, Bonn, Germany
3 - Astronomick'y 'ustav, Akademie vv{e}d v{C}esk'e republiky, Ondv{r}ejov, Czech Republic
4 - University of Sheffield, Sheffield, UK
5 - Astrophysikalisches Institut Potsdam, Potsdam, Germany
6 - Observat'orio Nacional, Rio de Janeiro, Brazil

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.

Reference: To be published in MNRAS Letters
Status: Manuscript has been accepted


Comments: 5 pages, 4 figures, 2 tables