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

Understand

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.