FS Canis Majoris variable

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An FS Canis Majoris variable (FS CMa star) is a type of eruptive variable star. The class of variable stars are named after its prototype, FS Canis Majoris.

They are somewhat poorly understood, most likely binary star systems in which mass exchange is ongoing or has recently happened, and most likely consist of at least one B-type main-sequence stars in a dust envelope. They undergo irregular light variations over long periods of time, with magnitude variation of approximately 2 magnitudes. The hydrogen emission lines from these stars are much stronger than in normal Be stars, and certain forbidden lines are present in the spectrum as well so they are classified as B[e] stars.[1]

FS CMa stars are rare and it has been difficult to determine their properties well enough to determine what causes their unusual character. Several have been detected in massive star clusters and this has ruled out some theories about their origin. The preferred explanation is still for a binary origin, possibly as the result of stellar mergers.[2]


  1. ^ Otero, S. A.; Watson, C.; Wils, P. "Variable Star Type Designations in the VSX". AAVSO Website. American Association of Variable Star Observers. Retrieved 17 December 2014.
  2. ^ de la Fuente, D.; Najarro, F.; Trombley, C.; Davies, B.; Figer, D. F. (2015). "First detections of FS Canis Majoris stars in clusters. Evolutionary state as constrained by coeval massive stars". Astronomy and Astrophysics. 575: A10. arXiv:1412.7988. Bibcode:2015A&A...575A..10D. doi:10.1051/0004-6361/201425371.