The X-ray emission of Tau Sco, Bo V, and the problems posed for embedded shock models

Main sequence OB-stars are useful for testing X-ray source models, because the mass loss rates are low as compared to those of the OB supergiants and the Of stars hence the winds are optically thin at nearly all frequencies. Tau Sco is a very well studied B0 V star. The discovery of the resonance doublet of O VI (1030 Å) in its Copernicus satellite spectrum led to the recognition of the now well known "superionization" problem. This led to the prediction that O and B stars would be X-ray sources.