The Spectra of Type II Cepheids. III. The Hα Line and Helium Emission in Long-Period Stars

We have obtained Hα profiles from 175 spectra of 37 Cepheids with periods longer than 8 days. About two-thirds of the stars are likely type II Cepheids. In contrast to the situation among short-period stars, the velocity of Hα relative to the metal-line spectrum is not a useful parameter for distinguishing type I and type II Cepheids. On the other hand, at periods longer than 11 days and shorter than 34 days strong emission is observed in many stars and appears to be a good discriminator of type. On this basis we identify one probable type I Cepheid at a large distance from the Galactic plane. We have found He λ5876 emission in seven Cepheids among the long-period stars discussed here and in one star with a short period, bringing to nine the number of type II Cepheids known to exhibit He emission.

Based in part on observations obtained with the Apache Point Observatory 3.5 m telescope, which is owned and operated by the Astrophysical Research Consortium.