THE ABUNDANCE OF INTERSTELLAR OXYGEN TOWARD ORION - EVIDENCE FOR RECENT INFALL

We present high S/N (> 800) Goddard High-Resolution Spectrograph obser vations of the weak interstellar O I] lambda 1356 absorption in the lo w-density sight lines toward iota Ori and kappa Ori. By comparing thes e data with observations toward more reddened stars, we find no eviden ce of density-dependent depletion from the gas phase for oxygen. The d erived total oxygen abundance (gas plus grains) toward iota Ori and ka ppa Ori is consistent with stellar and nebular determinations in Orion at a level that is one-half the solar value. We speculate that the O/ H abundance ratio is lower in Orion compared to the Sun because the lo cal Milky Way has suffered a recent infall of metal-poor material, per haps from the Magellanic Stream.