Canis Majoris, H.D. 150135, H.D. 159176, H.D. 199579, H.D. 164794, H.D. 167771, H.D. 165052, give a pure absorption spectrum, containing the Balmer series of hydrogen, the lines of Si+++, the Pickering and “4686” lines of He+, and the N++ line at 4097. The stars are mentioned in order of increasing ionization, with He+ rising in intensity. The other lines mentioned are clearly beyond their maximum, and fall progressively in strength. The stars mentioned probably represent successive steps in a sequence with rising temperature, connecting directly with Class
, and ranging from 25,000° to 35,000°.
This sequence of
stars would form a simple and explicable series if it were an isolated group. There are, however, other stars, with spectra so similar to those of the series just quoted that there can be no doubt of a close relationship—they display absorption lines due to the same elements with about the same relative intensities—but emission lines tend to occur in various parts of the spectrum. 29 Canis Majoris,
Muscae, and
