The Spectra of Type II Cepheids. II. The Hα Line in Intermediate-Period Stars

We present 98 Hα profiles for 21 pulsating variable stars with periods from 3 to 8 days. The strength, depth, and shape of Hα vary throughout the cycles of the stars in a way consistent with the temperature changes. Otherwise, they are quite uniform among all the stars, with a single exception. In FM Del, Hα is weaker and has a smaller central depth than in the other stars. This and the wavelength shifts of the core are attributed to incipient emission. The differential velocity of Hα relative to the metal lines is less than 25 km s^-1 for all the stars except QY Cyg, FM Del, and EF Tau. We suggest that this indicates that only these stars are type II Cepheids despite the large distances of some of the others from the Galactic plane.

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.