In keeping with earlier studies of a smaler group of stars, we find that most objects with temperatures below 40,000K have nearly pure H atmospheres, while the majority of hotter stars contain significant quantities of heavier elements. However, with the enlarged sample we are able to fill in much more detail. In contrast to earlier work we find a significant number of objects with pure H atmospheres above 40,000K indicating that the EUV sample is biased to objects with lower opacity and higher mass, as expected. Nevertheless, all the stars hotter than 55,000K contain significant quantities of heavy elements. A steep rise in opacity can be seen at 54,000K, which we interpret as arising from the appearance of significant quantities of radiatively supported Fe and other Fe-group elements.
Arrows depict upper limits.