SIMBAD references

We report the major element as well as the oxygen, magnesium, and silicon isotope composition of a unique presolar silicate grain found in the fine-grained fraction of the Antarctic CR2 chondrite Graves Nunataks 95229. The grain is characterized by an extremely high ¹⁷O/¹⁶O ratio (6.3±0.2x10^–3) relative to solar values, whereas its ¹⁸O/¹⁶O ratio is solar within measurement uncertainty. It also shows enrichments in ^25,26Mg and a significant excess in ³⁰Si relative to solar system compositions, with δ²⁵Mg = 79 ± 21‰, δ²⁶Mg = 70±20‰, and δ³⁰Si = 379±92‰. This isotopic composition is consistent with an origin in the ejecta of a ∼1.3-1.4 M_☉ ONe nova with large contributions of material from a main-sequence companion star of roughly solar metallicity. However, many details of the stellar source remain undetermined, owing to the uncertainties of current nova nucleosynthesis models.

Auger electron spectroscopic analyses identify O, Mg, Si, and Fe as the grain's major constituents. Its (Mg+Fe)/Si atomic ratios are lower than that of olivine and correspond on average to Fe-Mg-pyroxene. A complex texture and heterogeneous major element distribution within the grain attest to condensation under non-equilibrium conditions, which is consistent with the proposed nova origin.