The chemical composition of the Orion star forming region. III. C, N, Ne, Mg, and Fe abundances in B-type stars revisited
Context. Early B-type stars are invaluable indicators of elemental abundances of their birth environments. In contrast to the surrounding neutral interstellar matter (ISM) and H ii regions, their chemical composition is unaffected by depletion onto dust grains and the derivation of different abundances from recombination and collisional lines. In combination with ISM or nebular gas-phase abundances, they facilitate the otherwise inaccessible dust-phase composition to be constrained.
Aims: We determine precise abundances of C, N, Mg, Ne, and Fe in early B-type stars in the Orion star-forming region to: a) review previous determinations using a self-consistent quantitative spectral analysis based on modern stellar atmospheres and recently updated model atoms; b) complement our previous results for oxygen and silicon; and c) establish an accurate and reliable set of stellar metal abundances to constrain the dust-phase composition of the Orion H ii region.
Methods: A detailed, self-consistent spectroscopic study of a sample of 13 narrow-lined B0 V-B2 V stars in Ori OB1 is performed. High-quality spectra obtained with FIES at the NOT are analysed using both a hybrid non-local thermodynamic equilibrium (non-LTE) method (i.e., classical line-blanketed LTE model atmospheres and non-LTE line formation) and line-profile fitting techniques, validating the approach by comparison with previous results obtained using line-blanketed non-LTE model atmospheres and a curve-of-growth analysis.
Results: The two independent analysis strategies provide consistent results for basic stellar parameters and the abundances of oxygen and silicon. The extended analysis to C, N, Mg, Ne, and Fe finds a high degree of chemical homogeneity, with the 1σ-scatter typically being 0.03-0.07 dex around the mean for the various elements. The present-day abundances of B-type stars in Ori OB1 are compatible at similar precision with cosmic abundance standard values as recently established from early-type stars in the solar neighbourhood and also with the Sun.
Astronomy and Astrophysics
- Pub Date:
- August 2011
- stars: abundances;
- stars: atmospheres;
- stars: fundamental;
- open clusters and associations: general;
- Astrophysics - Solar and Stellar Astrophysics;
- Astrophysics - Astrophysics of Galaxies
- 14 pages, 7 figures. Recommended for acceptance in A&