BORON ABUNDANCES OF B-STARS OF THE ORION ASSOCIATION

The boron abundance of four B-type stars from the Orion association ha s been determined from Goddard High Resolution Spectrograph (GHRS)/Hub ble Space Telescope (HST) spectra covering the B II 1362 Angstrom reso nance line. After correction for large non-LTE effects, the mean boron abundance is similar to the meteoritic abundance, but a factor of 4 ( 0.6 dex) greater than published abundances of boron in interstellar ga s. This difference in boron abundance between young stars and gas is u nexplained. The Orion stars were selected by their oxygen abundances: two are enriched in oxygen by about 60% relative to the others. Analys is of the GHRS spectra shows that the O-rich stars are deficient in bo ron by about 250% (0.4 dex) relative to the O-poor stars. Then, if the differences in oxygen abundance reflect differing levels of contamina tion of the natal clouds with (O-rich) ejecta of local Type II superno vae, the ejecta were not enriched in boron synthesized by the v-proces s.