2019ApJ...871..114O

Terzan 5 is a complex stellar system in the Galactic bulge, harboring stellar populations (SPs) with very different iron content (Δ[Fe/H] ∼ 1 dex) and with ages differing by several gigayears. Here we present an investigation of its variable stars. We report on the discovery and characterization of three RR Lyrae stars. For these newly discovered RR Lyrae and for six Miras of known periods we provide radial velocity (RV) and chemical abundances from spectra acquired with X-SHOOTER at the Very Large Telescope. We find that the three RR Lyrae and the three short-period Miras (P < 300 days) have RV consistent with being Terzan 5 members. They have subsolar iron abundances and enhanced [α/Fe], well matching the age and abundance patterns of the 12 Gyr metal-poor SPs of Terzan 5. Only one, out of the three long-period (P > 300 days) Miras analyzed in this study, has an RV consistent with being a Terzan 5 member. Its super-solar iron abundance and solar-scaled [α/Fe] nicely match the chemical properties of the metal-rich SP of Terzan 5 and its derived mass nicely agrees with being several gigayears younger than the short-period Miras. This young variable is an additional proof of the surprisingly young subpopulation discovered in Terzan 5.