A Cosmic Abundance Standard: Chemical Homogeneity of the Solar Neighbourhood and the ISM Dust-Phase Composition
Norbert Przybilla (1), Maria-Fernanda Nieva (1,2), Keith Butler (3)
(1) Dr. Remeis-Observatory Bamberg, (2) MPI for Astrophysics Garching, (3) University Observatory Munich
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.
Reference: ApJ Letters, in press
Status: Manuscript has been accepted