FORMATION OF MOLECULAR OXYGEN AND OZONE ON AMORPHOUS SILICATES

Oxygen in the interstellar medium is seen in the gas phase, in ices (incorporated in H{sub 2}O, CO, and CO{sub 2}), and in grains such as (Mg{sub x} Fe{sub 1-x} )SiO{sub 3} or (Mg{sub x} Fe{sub 1-x} ){sub 2}SiO{sub 4}, 0 < x < 1. In this investigation, we study the diffusion of oxygen atoms and the formation of oxygen molecules and ozone on the surface of an amorphous silicate film. We find that ozone is formed at low temperature (<30 K), and molecular oxygen forms when the diffusion of oxygen atoms becomes significant, at around 60 K. This experiment, besides being the first determination of the diffusion energy barrier (1785 {+-} 35 K) for oxygen atoms on a silicate surface, suggests bare silicates as a possible storage place for oxygen atoms in low-A{sub v} environments

On Water Formation in the Interstellar Medium: Laboratory Study of the O+D Reaction on Surfaces

In the interstellar medium (ISM), an important channel of water formation is the reaction of atoms on the surface of dust grains. Here, we report on a laboratory study of the formation of water via the O+D reaction network. While prior studies were done on ices, as appropriate to the formation of water in dense clouds, we explored how water formation occurs on bare surfaces, i.e., in conditions mimicking the transition from diffuse to dense clouds (Av ~ 1-5). Reaction products were detected during deposition and afterward when the sample is brought to a high temperature. We quantified the formation of water and intermediary products, such as D2O2, over a range of surface temperatures (15-25 K). The detection of OD on the surface signals the importance of this reactant in the overall scheme of water formation in the ISM

ERRATUM: "FORMATION OF MOLECULAR OXYGEN AND OZONE ON AMORPHOUS SILICATES" (2012, ApJ, 756, 98)

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ERRATUM: “FORMATION OF MOLECULAR OXYGEN AND OZONE ON AMORPHOUS SILICATES” (2012, ApJ, 756, 98)

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Elephant fossil record from Italy: knowledge, problems, and perspectives.

The earliest occurrence of elephantines in Italy is in the middle Villafranchian (late Middle Pliocene; ca. 2.6 Ma), with a primitive representative of the mammoth lineage. In addition to this still poorly known taxon, four elephant species are clearly recognized in Plio-Pleistocene fossil mammal assemblages from the Italian peninsula: Mammuthus meridionalis, M. trogontherii, M. primigenius, and Elephas (Palaeoloxodon) antiquus. In Sicily, at least three different taxa are present during the Pleistocene:the dwarf E. falconeri, the medium sized E. (P.) ‘‘mnaidriensis’’, and a third poorly known large sized taxon, represented by isolated findings, in some cases apparently associated with E. (P.) ‘‘mnaidriensis’’. A number of specimens from Spinagallo and Luparello, of intermediate size between E. ‘‘mnaidriensis’’ and E. falconeri, suggest the occurrence in Sicily of a further elephant species. Sardinia records the only case of an endemic small sized Mammuthus species from the western Mediterranean. The Italian elephant fossil record clearly shows the influence of climatic, physiographic and paleogeographic conditions on the pattern of occurrence and dispersal of this mammal group in Southern Europe