INFERRED INITIAL²⁶Al/²⁷Al RATIOS IN PRESOLAR STARDUST GRAINS FROM SUPERNOVAE ARE HIGHER THAN PREVIOUSLY ESTIMATED

Abstract

We performed an in-depth exploration of the Al-Mg system for presolar graphite, SiC, and Si 3 N 4 grains found to contain large excesses of 26 ratios that, on average, are ∼1.5-2 times larger than the ratios previously reported for the grains. The majority of presolar graphite and SiC grains are heavily affected by Al contamination, resulting in large negative Mg Mg 26 24 d intercepts of the isochron lines. Al contamination is potentially due to etching of the grains' surfaces and subsequent capture of dissolved Al during the acid dissolution of their meteorite host rocks. From the isochron fits, the magnitude of Al contamination was quantified for each grain. The amount of Al contamination on each grain was found to be random and independent of grain size, following a uniform distribution with an upper bound at 59% contamination. The Al contamination causes conventional whole-grain estimates to underpredict the initial Al Al ratios greatly exceed those predicted in the He/C and He/N zones of SN models.

STELLAR ORIGINS OF EXTREMELY 13C- AND 15N-ENRICHED PRESOLAR SIC GRAINS: NOVAE OR SUPERNOVAE?

“…Although Al contamination could lower the initial 26 Al/ 27 Al ratios estimated for the grains, the inferred amount of Al contamination found in most SiC grains is only up to 65%, i.e., a factor of two higher at most (Groopman et al 2015), which generally agree with the amount of Al contamination found in the grain GAB, (Figure 2(b)). By mixing 13 C-and 15 N-enriched shells with H envelope material to match C Si and 44 Ti excesses, X grains are likely to have incorporated more material from deeper layers, e.g., from the C/Si zone (Pignatari et al 2013a).…”

Coordinated EDX and micro‐Raman analysis of presolar silicon carbide: A novel, nondestructive method to identify rare subgroup SiC

“…Thus, aluminum is one of the most abundant trace elements (up to several wt%) in presolar SiC grains, while the abundance of magnesium (prior to 26 Al decay to 26 Mg, τ 1/2 = 0.72 Ma) is more than two orders of magnitude lower (i.e., 27 Al/ 24 Mg > 100; Groopman et al. ; Liu et al. ).…”

“…Magnesium is not expected to condense into SiC during condensation, but aluminum is. Thus, aluminum is one of the most abundant trace elements (up to several wt%) in presolar SiC grains, while the abundance of magnesium (prior to 26 Al decay to 26 Mg, s 1/2 = 0.72 Ma) is more than two orders of magnitude lower (i.e., 27 Al/ 24 Mg > 100; Groopman et al 2015;Liu et al 2016). The expectation is that almost all magnesium in SiC grains comes from the decay of 26 Al.…”

Astrophysics with Radioactive Isotopes

“…Although our spectral resolution is not high enough to resolve the individual 13 C 16 O lines, and the S/N ratios are not very high, the χ 2 r value reflects the subsection 4.2, and again the error of the resulting 12 C/ 13 C ratio can be estimated to be about 10%. Here the carbon isotopic ratio is determined for the stellar atmosphere of a M dwarf star, comparing the measurement (red dots) with expectations for different ratios 12 Groopman et al (2015) for these references).…”