Ultraviolet spectral morphology of the O stars. II. The main sequence.

Abstract

A survey of the 1200-1900 A region in 49 spectra of types O3-B1 V, based upon IUE high-resolution data, is presented. Standard sequences of prominent spectral features are illustrated, and UV classification criteria are introduced. For the majority of the stars, there is an excellent correlation between the behavior of the UV features, both stellar-wind and photospheric, and the optical spectral types. However, a group of stars with weak winds for their types is isolated, including Theta Orionis C in the Orion Trapezium; they may be nearer to the zero-age main sequence than the typical class V objects. Several cases of enhanced winds are also found; the most pronounced of these is the frequently observed 'standard', Tau Scorpii.