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The chemical composition of the Orion star forming region. I. Homogeneity of O and Si abundances in B-type stars
Context. Recent accurate abundance analyses of B-type main sequencestars in the solar vicinity has shown that abundances derived from thesestellar objects are more homogeneous and metal-rich than previouslythought. Aims: We investigate whether the inhomogeneity ofabundances previously found in B-type stars in the Ori OB1 associationis real (hence a signature of enrichment of the newly formed stars in aninduced star formation scenario) or a consequence of intrinsic errorsinduced by the use of photometric indices to establish the stellarparameters prior to the abundance analysis. Methods: We obtaineda new (improved) spectroscopic data set comprising 13 B-type stars inthe various Ori OB1 associations, and performed a detailed,self-consistent spectroscopic abundance analysis by means of the modernstellar atmosphere code fastwind. Results: We detect systematicerrors in the stellar parameters determined previously which affect thederived abundances. Once these errors are accounted for, we find a highdegree of homogeneity in the O and Si abundances for stars in the fourOri OB1 subgroups. The derived abundances are in very good agreementwith recent determinations in other B-type stars in the solar vicinity.We also compare our results with those obtained for the Sun during theepoch of the ”solar crisis”, and the Orion nebula.Based on observations made with the Nordic Optical Telescope, operatedjointly on the island of La Palma by Denmark, Finland, Iceland, Norway,and Sweden, in the Spanish Observatorio del Roque de los Muchachos ofthe Instituto de Astrofisica de Canarias.Tables 5 to 18, and Fig. 8 areavailable in electronic form at http://www.aanda.org
| SANTIAGO 91, a right ascension catalogue of 3387 stars (equinox J2000).
The positions in right ascension of 3387 stars belonging to the Santiago67 Catalogue, observed with the Repsold Meridian Circle at Cerro Calan,National Astronomical Observatory, during the period 1989 to 1994, aregiven. The average mean square error of a position, for the wholeCatalogue, is +/-0.009 s. The mean epoch of the catalogue is 1991.84.
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