The nature of FS CMa stars as revealed by host young clusters

The nature and evolutionary state of the diverse objects displaying the B[e] phenomenon are reasonably known, except for a rare subtype named FS CMa stars. These are surrounded by compact disks of warm dust whose origin is unclear. Although the luminosity of these objects corresponds to main-sequence stars, mass loss rates derived from emission lines are 2 orders of magnitude larger than predicted by wind theory. Hitherto, FS CMa stars have been only found in isolation, which hinders the study of their nature. In this contribution, we present the discovery of FS CMa stars in two young Galactic clusters, which host Wolf-Rayet stars and OB supergiants. Membership to these coeval populations allows us to constrain the luminosity, circumstellar extinction and age of FS CMa stars in an unprecedented way. Due to their relatively low brightness when compared with coeval evolved massive stars, a high number of these stars may remain unnoticed in young clusters.