2013MNRAS.429.2852K

The early B supergiant Large Magellanic Cloud (LMC) star BI 108 is photometrically variable with a unique light curve; two strong periods are present in an almost precise 3:2 resonance. We collected spectroscopic data at the Very Large Telescope (VLT) with the Ultraviolet and Visual Echelle Spectrograph (UVES), sampling the supercycle of 10.733 d in 10 epochs. We find spectral signatures for an SB2 system consisting of two massive B1 supergiants orbiting at the orbital period of 5.366 d. The shorter periodicity resembles the light curve of an eclipsing binary with periodicity 3.578 d that is not detected in the data. We discuss possible causes for the short periodicity and conclude that the quadruple system is the more plausible hypothesis.