SIMBAD references

We present X-ray images of the high-mass star-forming region Cepheus OB3, in which we discover over 50 point sources, the majority of which are T Tauri stars. We use the ratio of high-mass to low-mass stars to constrain the initial mass function, and find that it is consistent with that for field stars. This supports the picture that there is little difference between high-mass and low-mass star-forming regions. The presence of low-mass stars between the high-mass stars and the molecular cloud they are ionizing argues against mechanisms whereby heating of the cloud inhibits low-mass star formation. Finally, the efficiency of star formation in this region is shown to be of the order of a few per cent.