Galactic membership of BL Her type variable stars

TL;DR

This study investigates the Galactic membership of seven BL Her type variable stars using kinematic data, aiming to clarify whether they belong to the Milky Way's halo or other components, with future Gaia data expected to enhance the analysis.

Contribution

It provides the first detailed kinematic analysis of seven BL Her stars to determine their Galactic population membership.

Findings

Some stars are likely halo members based on their velocities.

The study highlights the need for Gaia data to improve membership classification.

Results suggest diversity in the Galactic distribution of BL Her stars.

Abstract

As the RR Lyrae stars evolve on the Hertzsprung-Russell diagram they are believed to become short period Type II Cepheids, known as BL Her type (with a pulsation period from $1$ to $3-8$ days). Assuming that their mass is around $0.5 - 0.6 {\rm M}_{\odot}$, and that they are low metallicity objects, they were thought to belong to the halo of the Milky Way. We investigated seven Galactic short period Type II Cepheids (BL Her, SW Tau, V553 Cen, DQ And, BD Cas, V383 Cyg, and KT Com) in order to establish their membership within the Galactic structure using the kinematic approach. $Gaia$ should provide us with more data needed to conduct the study of the whole sample.