Oxygen-rich stardust grains from novae

Abstract

Stardust grains which have condensed from nova ejecta are exceedingly rare in meteorites. Principally through proton captures, novae are efficient producers of the stable isotopes 13C, 15N, and 17O, as well as radioactive isotopes such as 22Na and 26Al. To date, primarily carbonaceous phases of stardust grains (e.g., SiC and graphite), have been purported to have a nova origin. Conversely, as material ejected in nova explosions is O-rich, it remains a puzzle why to date mostly carbonaceous nova grain candidates have been discovered. O-rich stardust grains with 17O/16O ratios significantly greater than 0.004, the predicted maximum value that can be reached in low- and intermediate-mass AGB and RGB stars, have been proposed to have a nova origin. The O isotopic compositions of many of these grains can be fairly well matched by CO nova model predictions. However, two grains whose Mg-Al compositions had been determined have much smaller excesses of the heavy Mg isotopes than predicted by nova models, which miss the grain data by up to several orders of magnitude. New nova models computed with recently updated reaction rates further complicate this overall picture. © Copyright owned by the author(s).