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Title: Molybdenum Isotopes in Presolar Silicon Carbide Grains: Details of s -process Nucleosynthesis in Parent Stars and Implications for r - and p -processes

Journal Article · · The Astrophysical Journal (Online)
ORCiD logo [1]; ORCiD logo [2]; ORCiD logo [3]; ORCiD logo [1]; ORCiD logo [4]; ORCiD logo [1]
  1. Univ. of Chicago, IL (United States); Chicago Center for Cosmochemistry, Chicago, IL (United States)
  2. Univ. of Chicago, IL (United States); Chicago Center for Cosmochemistry, Chicago, IL (United States); Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  3. Max Planck Society, Mainz (Germany)
  4. Univ. of Chicago, IL (United States); Chicago Center for Cosmochemistry, Chicago, IL (United States); Argonne National Lab. (ANL), Lemont, IL (United States)
+ Show Author Affiliations

We have analyzed molybdenum isotopes, together with strontium and barium isotopes, in 18 presolar silicon carbide grains using the Chicago Instrument for Laser Ionization (CHILI), a resonance ionization mass spectrometer. All observed isotope ratios can be explained by mixtures of pure s-process matter with isotopically solar material. Grain residues were subsequently analyzed for carbon, nitrogen, silicon, and sulfur isotopes, as well as a subset for 26Al–26Mg systematics using the NanoSIMS. These analyses showed that all but one grain are mainstream grains, most probably coming from low-mass asymptotic giant branch (AGB) stars. One grain is of the AB type, for which the origin is still a matter of debate. The high precision of molybdenum isotope measurements with CHILI provides the best estimate to date for s-process molybdenum made in low-mass AGB stars. The average molybdenum isotopic abundances produced by the s-process found in the analyzed mainstream SiC grains are 0% 92Mo, 0.73% 94Mo, 13.30% 95Mo, 36.34% 96Mo, 9.78% 97Mo, 39.42% 98Mo, and 0.43% 100Mo. Solar molybdenum can be explained as a combination of 45.9% s-process, 30.6% r-process, and 23.5% p-process contributions. Moreover, the observed variability in the individual grain data provides insights into the variability of conditions (neutron density, temperature, and timescale) during s-process nucleosynthesis in the grains' parent stars, as they have subtle effects on specific molybdenum isotope ratios. Lastly, the results indicate that the ratio between p- and r-process molybdenum in presolar SiC from many different types of parent stars is Mo p /Mo r = 0.767, the value inferred for the solar system and consistent with what has been found in bulk samples and leachates of primitive meteorites.

Research Organization:
Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
Sponsoring Organization:
USDOE National Nuclear Security Administration (NNSA)
Grant/Contract Number:
AC52-07NA27344
OSTI ID:
1544506
Report Number(s):
LLNL-JRNL-768104; 958808
Journal Information:
The Astrophysical Journal (Online), Vol. 877, Issue 2; ISSN 1538-4357
Publisher:
Institute of Physics (IOP)Copyright Statement
Country of Publication:
United States
Language:
English

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  • Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, Vol. 12, Issue 2 https://doi.org/10.1116/1.579255
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Cited By (4)

Presolar Silicon Carbide Grains of Types Y and Z: Their Molybdenum Isotopic Compositions and Stellar Origins journal August 2019
Isotopes of Barium as a Chronometer for Supernova Dust Formation journal November 2019
Isotopic Signatures of Supernova Nucleosynthesis in Presolar Silicon Carbide Grains of Type AB with Supersolar 14 N/ 15 N Ratios journal December 2019
Presolar Silicon Carbide Grains of Types Y and Z: Their Molybdenum Isotopic Compositions and Stellar Origins text January 2019

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