Abstract
Abstract The isotopic compositions of ruthenium (Ru) are measured from presolar silicon carbide (SiC) grains. In a popular scenario, the presolar SiC grains formed in the outskirt of an asymptotic giant branch (AGB) star, left the star as a stellar wind, and joined the presolar molecular cloud from which the solar system formed. The Ru isotopes formed inside the star, moved to the stellar surface during the AGB phase, and were locked into the SiC grains. Following this scenario, we analyze the Nucleosynthesis Grid (NuGrid) data, which provide the abundances of the Ru isotopes in the stellar wind for a set of stars in a wide range of initial masses and metallicities. We apply the C > O (carbon abundance larger than the oxygen abundance) condition, which is commonly adopted for the condition of the SiC formation in the stellar wind. The NuGrid data confirm that SiC grains do not form in the winds of massive stars. The isotopic compositions of Ru in the winds of low-mass stars can explain the measurements. We find that lower-mass stars (1.65 M ☉ and 2 M ☉) with low metallicity (Z = 0.0001) can explain most of the measured isotopic compositions of Ru. We confirm that the abundance of 99 Ru inside the presolar grain includes the contribution from the in situ decay of 99 Tc. We also verify our conclusion by comparing the isotopic compositions of Ru integrated over all the pulses with those calculated at individual pulses.
Highlights
Our solar system or a planetary system in general formed from a molecular cloud that had collapsed due to its own gravity
We obtain the isotopic compositions of Ru by analyzing the NuGrid data and compare them with those measured from the presolar silicon carbide (SiC) grains
The NuGrid data confirm that the C>O condition required for the SiC grain formation is not satisfied in the wind of any massive star, regardless of the metallicity
Summary
Our solar system or a planetary system in general formed from a molecular cloud that had collapsed due to its own gravity. The molecular cloud from which the solar system formed was under the influence of its environments. The grains in the molecular could affect the evolution of the solar system such as formation of meteorites and terrestrial planets (Huss 1988). Some of the grains that existed when the solar system formed can be found even at the present time because they have been able to survive the destruction process during the history of the solar system. These survived grains, often called presolar grains, are found within meteorites (Lodders & Amari 2005) and provide information on the early times
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