Stellar multipilicity in the {\sigma} Orionis cluster: a review

Abstract

The nearby, young, extinction-free {\sigma} Orionis cluster is acknowledged as a cornerstone for studying the stellar and substellar formation and evolution, especially at very low masses. However, the relatively limited knowledge of multiplicity in the cluster is dispersed among numerous papers and proceedings with very different aims and, therefore, is difficult to apprehend even for researchers in the subject. Here, I review comprehensively the sexdecuple system {\sigma} Ori in the central arcminute, and all close (rho = 0.4-4 arcsec) and wide (rho > 4 arcsec) binaries, triples, hierarchical multiples, and spectroscopic binaries in the cluster that have been reported in the literature until 2014. I conclude with a brief enumeratation of the next steps that should be taken in the near future for having a clear picture of the multiplicity in the {\sigma} Orionis cluster.