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

TL;DR

This study detects enhanced $^{13}$C in two B[e] supergiants in the Large Magellanic Cloud through $^{13}$CO emission, confirming their evolved, post-main sequence status and demonstrating a new method for identifying such stars.

Contribution

First direct detection of $^{13}$C enhancement in B[e] supergiants using $^{13}$CO emission, confirming their evolved nature and validating theoretical predictions.

Findings

Both stars show strong $^{13}$CO emission.

$^{13}$C enhancement aligns with stellar evolution models.

Method enables identification of evolved 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.