In Situ Isotopic Analysis of Presolar Graphite Challenges Stellar Models
- 1The University of Chicago
- 2Chicago Center for Cosmochemistry
- 3Max Planck Institute for Chemistry
Abstract
We have analyzed zirconium, molybdenum, and barium isotopes for the first time in situ in two presolar graphite grains found in polished thin sections from the CM2 meteorites Maribo and Murchison. Both grains most likely originated in low-mass, low-metallicity AGB stars. The Maribo grain has almost pure s -process molybdenum in a subgrain, challenging AGB star models that assume homogenization of s -process material in the convective stellar envelope prior to grain condensation. Either this grain formed in a chemically and isotopically distinct high-density region or after its parent star had already lost its envelope. Furthermore, neutrons from the ²² Ne( α , n ) ²⁵ Mg reaction were only marginally captured by ⁹⁵ Zr in both grains’ parent stars, which further challenge stellar models and the theoretically derived neutron-capture cross section of ⁹⁵ Zr. Finally, both grains showed contamination with molybdenum of solar composition in some regions of the grains, probably from aqueous alteration on their parent asteroids, emphasizing the importance of depth-resolved isotope studies.
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BibTeX
@article{stephan2026situ,
title = {{In Situ Isotopic Analysis of Presolar Graphite Challenges Stellar Models}},
author = {Thomas Stephan and Jan Leitner and Andrew M. Davis and Julie M. Korsmeyer and Gavin Fowler and Liv Mumma and Andrew Regula},
journal = {The Astrophysical Journal},
year = {2026},
month = nov,
doi = {10.3847/1538-4357/aeb016},
url = {https://iopscience.iop.org/article/10.3847/1538-4357/aeb016},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - In Situ Isotopic Analysis of Presolar Graphite Challenges Stellar Models
AU - Thomas Stephan
AU - Jan Leitner
AU - Andrew M. Davis
AU - Julie M. Korsmeyer
AU - Gavin Fowler
AU - Liv Mumma
AU - Andrew Regula
PY - 2026
DA - 2026/11/04
JO - The Astrophysical Journal
DO - 10.3847/1538-4357/aeb016
UR - https://iopscience.iop.org/article/10.3847/1538-4357/aeb016
AB - We have analyzed zirconium, molybdenum, and barium isotopes for the first time in situ in two presolar graphite grains found in polished thin sections from the CM2 meteorites Maribo and Murchison. Both grains most likely originated in low-mass, low-metallicity AGB stars. The Maribo grain has almost pure s -process molybdenum in a subgrain, challenging AGB star models that assume homogenization of s -process material in the convective stellar envelope prior to grain condensation. Either this grain formed in a chemically and isotopically distinct high-density region or after its parent star had already lost its envelope. Furthermore, neutrons from the ²² Ne( α , n ) ²⁵ Mg reaction were only marginally captured by ⁹⁵ Zr in both grains’ parent stars, which further challenge stellar models and the theoretically derived neutron-capture cross section of ⁹⁵ Zr. Finally, both grains showed contamination with molybdenum of solar composition in some regions of the grains, probably from aqueous alteration on their parent asteroids, emphasizing the importance of depth-resolved isotope studies.
SN - 1538-4357
SN - 0004-637X
ER -