Spectroscopic observations of O-type stars. V. The hydrogen lines and lambda4686 He II

We present data concerning the A4686 He ii and Ha lines, including selected profiles, in a number of 0-type stars. We now find, in agreement with Walborn, that the emission-line behavior of A4686 tends to correlate with luminosity. Both it and Ha come into emission if extended envelopes are present and it is this physical condition that is related to luminosity. Envelopes invariably appear in 0-type stars if Mv is brighter than about -6. The observed emission strength of both lines and the extent of the envelope is relatively insensitive to luminosity. The scatter in the relation between these parameters is large and we feel one cannot predict Mv from the line strength more accurately than about 10.5 mag. We also call attention to a group of stars that we classify as 0e and Oef (the latter group identical to the Onfp designation of Walborn) in which characteristic "double" emission lines are observed in either the hydrogen lines, or in A4686, respectively. We believe the double emission is the result of a combination of roughly central emission and central absorption in the line profile. These profiles can be produced by stars having envelopes with appreciable rotation. The Oe and Oef stars share the characteristic of having rapid rotation, and luminosity somewhat near the main sequence. They do not follow the luminosity-envelope relationship observed for the Of stars. We believe the Oe and Oef stars are a continuation of the Be phenomenon to the earliest spectral types, or at least the manifestation of rapid rotation affecting the atmosphere. Sabject headings: early-type stars - emission-line stars - line profiles - spectral classification - Of-type stars