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Chemical evolution of the Orion association. I - The oxygen abundance of main-sequence B stars
Cunha, Katia; Lambert, David L.
AA(Texas Univ., Austin), AB(Texas Univ., Austin)
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 399, no. 2, p. 586-598. (ApJ Homepage)
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NASA/STI Keywords:
B Stars, Chemical Evolution, Main Sequence Stars, Oxygen Spectra, Abundance, Nonequilibrium Thermodynamics, Open Clusters
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Oxygen abundances are presented from LTE and non-LTE analyses of O II lines in spectra of 18 B mainsequence stars of the four subgroups comprising the Orion association. The lowest abundances are found in the oldest subgroups (Ia and Ib). The youngest subgroup Id, the Trapezium cluster, and some stars of the slightly older Ic subgroup seem to have an abundance that is up to about 40 percent higher. It is suggested that this enrichment resulted from the mixing of supernovae ejecta from the Ic subgroup with those adjacent portions of the dense molecular cloud that subsequently collapsed to form the Trapezium cluster. These stellar analyses confirm published abundance analyses of the H II region's emission lines that show Orion to have an oxygen abundance that is less than that of the Sun: the mean LTE/NLTE abundances are log epsilon(O) = 8.67/8.65 +/- 0.12 for the 18 stars whereas the solar abundance is log epsilon(O) = 8.93.

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