The terzan 5 puzzle: Discovery of a third, metal-poor component

Abstract

We report on the discovery of three metal-poor giant stars in Terzan 5, a complex stellar system in the Galactic bulge, known to have two populations at [Fe/H] = -0.25 and +0.3. For these three stars we present new echelle spectra obtained with NIRSPEC at Keck II, which confirm their radial velocity membership and provide an average [Fe/H] = -0.79 dex iron abundance and [α/Fe] = +0.36 dex enhancement. This new population extends the metallicity range of Terzan 5 to 0.5 dex more metal poor, and it has properties consistent with having formed from a gas polluted by core-collapse supernovae. © 2013. The American Astronomical Society. All rights reserved.