New constraints on the chemical evolution of the solar neighbourhood and Galactic disc(s)

TLDR

The study re‑analyses the Geneva‑Copenhagen survey using improved infrared‑flux temperatures and a refined metallicity scale to enable more accurate age determinations and a first‑time alpha‑element proxy for dissecting the thin and thick discs. The authors calibrate metallicities against high‑resolution spectroscopy and open clusters, match the new scales to theoretical isochrones for Bayesian age analysis, and derive an alpha proxy from Stromgren photometry. Compared to earlier work, the revised sample shows stars that are on average 100 K hotter and 0.1 dex more metal‑rich, shifting the metallicity distribution peak to the solar value, and reveals an old, mildly alpha‑enhanced thick‑disc population extending to super‑solar metallicities, providing the largest unbiased dataset for constraining Milky Way disc evolution.

Abstract

We present a re-analysis of the Geneva-Copenhagen survey, which benefits from the infrared flux method to improve the accuracy of the derived stellar effective temperatures and uses the latter to build a consistent and improved metallicity scale. Metallicities are calibrated on high-resolution spectroscopy and checked against four open clusters and a moving group, showing excellent consistency. The new temperature and metallicity scales provide a better match to theoretical isochrones, which are used for a Bayesian analysis of stellar ages. With respect to previous analyses, our stars are on average 100 K hotter and 0.1 dex more metal rich, which shift the peak of the metallicity distribution function around the solar value. From Stromgren photometry we are able to derive for the first time a proxy for alpha elements, which enables us to perform a tentative dissection of the chemical thin and thick disc. We find evidence for the latter being composed of an old, mildly but systematically alpha-enhanced population that extends to super solar metallicities, in agreement with spectroscopic studies. Our revision offers the largest existing kinematically unbiased sample of the solar neighbourhood that contains full information on kinematics, metallicities, and ages and thus provides better constraints on the physical processes relevant in the build-up of the Milky Way disc, enabling a better understanding of the Sun in a Galactic context.