A cosmic abundance standard: chemical homogeneity of the solar neighbourhood and the ISM dust-phase composition

TL;DR

This study establishes a precise, homogeneous cosmic abundance standard for the solar neighbourhood using B-type stars, aligning with recent solar models and constraining ISM dust composition.

Contribution

It provides the first high-precision, homogeneous chemical abundance standard for the local universe based on early B-type stars, improving upon previous heterogeneous measurements.

Findings

Chemical composition more metal-rich and homogeneous than previous estimates.

RMS scatter of ~10% in abundances across stars, matching ISM gas-phase data.

Proposed mass fractions for hydrogen, helium, and metals consistent with recent solar models.

Abstract

A representative sample of unevolved early B-type stars in nearby OB associations and the field is analysed to unprecedented precision using NLTE techniques. The resulting chemical composition is found to be more metal-rich and much more homogeneous than indicated by previous work. A rms scatter of ~10% in abundances is found for the six stars (and confirmed by six evolved stars), the same as reported for ISM gas-phase abundances. A cosmic abundance standard for the present-day solar neighbourhood is proposed, implying mass fractions for hydrogen, helium and metals of X=0.715, Y=0.271 and Z=0.014. Good agreement with solar photospheric abundances as reported from recent 3D radiative-hydrodynamical simulations of the solar atmosphere is obtained. As a first application we use the cosmic abundance standard as a proxy for the determination of the local ISM dust-phase composition, putting tight observational constraints on dust models.