361 Hertzsprung-Russell diagram in Orion

A comparison of the locations of the stars in the H-R diagram with the non-magnetic and magnetic pre-main-sequence evolutionary tracks indicates an age of 1-2Myr. The magnetic pre-main-sequence evolutionary tracks can better explain the luminosities of the low-mass stars. In the H-R diagram, the cluster exhibits a large luminosity spread ({sigma}(LogL*/L{sun})~0.3).

By collecting a sample of 14 clusters/groups with different ages, we find that the luminosity spread tends to be constant ({sigma}(LogL*/L{sun})~0.2-0.25) after 2Myr, which suggests that age spread is not the main cause of the luminosity spread. There are ~0.1dex larger luminosity spreads for the younger clusters, e.g., the Trapezium cluster, than the older clusters, which can be explained by the starspots, accretion history, and circumstellar disk orientations.