The sudden appearance of CO emission in LHA 115-S 65

TL;DR

This paper reports the unexpected detection of CO emission in the B[e] supergiant LHA 115-S 65, suggesting rapid changes in its circumstellar environment and potential evolutionary links to luminous blue variables.

Contribution

It presents the first detection of CO band head emission in LHA 115-S 65, highlighting variability in molecular emission in B[e] supergiants and proposing a possible disk density build-up mechanism.

Findings

CO emission appeared suddenly after previous non-detections

Variability observed in molecular emission of B[e] supergiants

Suggests an evolutionary connection between B[e] supergiants and LBVs

Abstract

Molecular emission has been detected in several Magellanic Cloud B[e] supergiants. In this Letter, we report on the detection of CO band head emission in the B[e] supergiant LHA 115-S 65, and present a K-band near-infrared spectrum obtained with the Spectrograph for INtegral Field Observation in the Near-Infrared (SINFONI; R=4500) on the ESO VLT UT4 telescope. The observed molecular band head emission in S 65 is quite surprising in light of a previous non-detection by McGregor et al. 1989, as well as a high resolution (R=50000) Gemini/Phoenix spectrum of this star taken nine months earlier showing no emission. Based on analysis of the optical spectrum by Kraus et al. 2010, we suspect that the sudden appearance of molecular emission could be due to density build up in an outflowing viscous disk, as seen for Be stars. This new discovery, combined with variability in two other similar evolved massive stars, indicates an evolutionary link between B[e] supergiants and LBVs.