高能暂现源 · 每日文献综述

Near-IR spectra of a homogeneous sample of 15 red giants in the Galactic nuclear star cluster, within 1.5 pc of SgrA*, have been acquired with X-shooter at the Very Large Telescope. From these spectra, line-of-sight radial velocities and chemical abundances of iron, carbon, oxygen, and other alpha and light elements have been derived. By combining radial velocities from this study and proper motions from the literature, we computed the orbits of these stars, finding that they have been confined within 12 pc from SgrA* for their entire lifetime, thus strongly suggesting an in situ formation and evolution. Iron abundances between half and twice solar; approximately solar-scaled values within ±0.1 dex for α-elements, Ti, and V; some enhancement of [Na/Fe], [K/Fe], and [Al/Fe]; and some depletion of [C/Fe] with respect to the solar ratios have been measured. The inferred chemical abundance distributions are consistent with a formation from a gas enriched by type II and type I supernovae (SNe) over a prolonged timescale, closely matching those of the metal-rich populations of the inner bulge field and other complex stellar systems like Terzan 5 and Liller 1.