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

TL;DR

This study analyzes high-resolution spectra of short-period Type II Cepheids, revealing two distinct metallicity groups and proposing a new subclass called UY Eri stars, which resemble halo globular cluster variables.

Contribution

The paper identifies a new subclass of metal-poor Type II Cepheids called UY Eri stars, distinguished by their lower metallicities and similarities to halo globular cluster variables.

Findings

Two metallicity groups among short-period Type II Cepheids.

Proposal of UY Eri as a new subclass of metal-poor Cepheids.

Globular clusters with [Fe/H] > -1.0 rarely host Type II Cepheids.

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.