Research Papers in Physics and Astronomy

 

Date of this Version

December 2004

Comments

Published in The Astronomical Journal 128, pp. 2988-2996 (December 2004). Copyright 2004 by the University of Chicago Press and the American Astronomical Society. Journal homepage = http://www.journals.uchicago.edu/AJ/
Reproduced by permission of the AAS.

Abstract

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.

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