Ion imaging of small interstellar grains

Details Ion imaging of small interstellar grains Ion imaging of small interstellar grains

Publishing date

Jul 1994

URL

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29r.474h&link_type=abstract

Journals

Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 474-475

Science

Computer Science

Additional info 2

7

Additional info 3

Chemical Composition, Grain Size, Interstellar Matter, Isotopes, Murchison Meteorite, Anomalies, Image Processing, Ion Probes, Silicon Carbides

Type

Scientific paper

Abstract

We report results for elemental and isotopic ratios of approximately 1400 grains from Murchison SiC separate KJE (average size 1.14 micron) obtained by ion imaging with the University of Bern ion microprobe. The technique of ion imaging has been successfully applied to larger grains. In order to get a better characteriztion of small interstellar grains we were searching for isotopically exotic subsets of grains such as SiC grains X, oxides, and the recently discovered nitrides. For this purpose we acquired digitized isotopic images of C-12, O-16, O-18, (12)C(14)N, Si-28, and Si-30 at low mass resolution. Each imaging run on our KJE sample typically recorded 10-20 individual grains. As the grains of our KJE sample are small the ion imaging analysis time was kept short in order to preserve sufficient material (greater than or approximately 90%) for subsequent high-mass resolution analyses of the selected grains. Since isotopic in O-18/O-16 of interstellar oxide grains in most cases are known to be relatively small, only grains with comparatively large isotopic anomalies can be detected. So far we measured approximately 1100 SiC grains. Seven of them have delta(S-30) values between -530% and -390%, the signature of the SiC grains X. The secondary ion signals of about 300 grains were clearly dominated by O. Six of them fall within our selection range for O-isotopic compositions, thus being potential candidates for interstellar oxide grains. In order to verify the isotopic signatures obtained by ion imaging we will analyze the C-, N- and Si-isotopic compositions of our probable SiC grains X as well as the O-isotopic compositions of our potential interstellar oxide grains at high-mass resolution.

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