Einstein observations of the Rosette nebula and the MON OB2 association.

Einstein IPC observations of the Rosette nebula and the Monoceros OB2 association reveal X-ray emission from individual O stars and from the central part of the Rosette nebula surrounding the O stars. The Mon OB2 stars are main-sequence stars and have lower X-ray luminosities than most other OB stars (primarily giants and supergiants) observed with Einstein, but still follow the approximately 10 to the -7th ratio of X-ray to bolometric flux. The diffuse nebula X-ray emission is coincident with the central radio minimum of the Rosette suggesting that hot gas originating from the central O stars is responsible for the diffuse X-rays and the thick hollow shell appearance of the Rosette H II region.