Orionis also appear to be very massive.[444]
The spectra of the stars of Class
differ widely among themselves, but they are signalized by the lines of ionized helium, which are normally observed only in this class and in the nebulae. In addition, the atoms of H, He, Mg+, C++, 0++, N++, and Si+++ are represented. The atmospheres of these stars are thus in a state of high ionization, which is attributed to high temperature, in harmony with the work already outlined in previous chapters. The spectra of the stars of Class
have been described by W. W. Campbell,[445] Miss Cannon,[446] Wright,[447] H. H. Plaskett,[448] J. S. Plaskett,[449] and the writer,[450] and the material upon which the present discussion is based will be found in the papers quoted.
Many of the
stars, such as