Stars and brown dwarfs, spatial distribution, multiplicity, X-rays,   discs, and the complete mass function of the sigma Orionis cluster
  The young sigma Orionis cluster in the Orion Belt is an incomparable site for studying the formation and evolution of high-mass, solar-like, and low-mass stars, brown dwarfs, and substellar objects below the deuterium burning mass limit. The first version of the Mayrit catalogue was a thorough data compilation of cluster members and candidates, which is regularly used by many authors of different disciplines. I show two new applications of the catalogue and advance preliminar results on very wide binarity and the initial mass function from 18 to 0.035 Msol in sigma Orionis. The making-up of a new version of the Mayrit catalogue with additional useful data is in progress. 
Jose A. Caballero