Metal-Poor Type II Cepheids with Periods Less Than Three Days

Abstract

We have analysed 10 high resolution spectra of Type II Cepheids with periods less than 3 days. We find that they clearly separate into two groups: those with near or slightly below solar metallicities, and those with [Fe/H] between --1.5 and --2.0. While the former are usually called BL~Her stars, we suggest that the latter be called UY~Eri stars. The UY~Eri subclass appears to be similar to the short period variables in globular clusters of the Galactic Halo. Globular clusters with [Fe/H] $\textgreater$ --1.0 almost never have Type II Cepheids.

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• On the separation between RR Lyrae and Type II Cepheids and their importance for distance determination: the case of $\omega$ Cen
• Effective temperatures of classical Cepheids from line-depth ratios in the H-band
• Kinematics of Type II Cepheids of the Galactic Halo
• Type II and anomalous Cepheids in the Kepler K2 mission