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Title: J-type Carbon Stars: A Dominant Source of 14 N-rich Presolar SiC Grains of Type AB

Abstract

Here, we report Mo isotopic data of 27 new presolar SiC grains, including 12 14N-rich AB ( 14N/ 15N > 440, AB2) and 15 mainstream (MS) grains, and their correlated Sr and Ba isotope ratios when available. Direct comparison of the data for the MS grains, which came from low-mass asymptotic giant branch (AGB) stars with large s-process isotope enhancements, with the AB2 grain data demonstrates that AB2 grains show near-solar isotopic compositions and lack s-process enhancements. The near-normal Sr, Mo, and Ba isotopic compositions of AB2 grains clearly exclude born-again AGB stars, where the intermediate neutron-capture process (i-process) takes place, as their stellar source. On the other hand, low-mass CO novae and early R- and J-type carbon stars show 13C and 14N excesses but no s-process enhancements and are thus potential stellar sources of AB2 grains. And because both early R-type carbon stars and CO novae are rare objects, the abundant J-type carbon stars (10%–15% of all carbon stars) are thus likely to be a dominant source of AB2 grains.

Authors:
 [1];  [2];  [2];  [1];  [1];  [1];  [3];  [4];  [4]
  1. Carnegi Inst. for Science, Washington, DC (United States). Dept. of Terrestrial Magnetism
  2. Univ. of Chicago, IL (United States). Dept. of Geophysical Sciences; Chicago Center for Cosmochemistry, Chicago, IL (United States)
  3. Univ. of Chicago, IL (United States). Dept. of Geophysical Sciences.; Chicago Center for Cosmochemistry, Chicago, IL (United States); Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). Nuclear and Chemical Sciences Division
  4. Univ. of Chicago, IL (United States). Dept. of Geophysical Sciences, Enrico Fermi Inst.; Chicago Center for Cosmochemistry, Chicago, IL (United States)
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE; National Aeronautics and Space Administration (NASA)
OSTI Identifier:
1414353
Report Number(s):
LLNL-JRNL-732767
Journal ID: ISSN 2041-8213
Grant/Contract Number:
AC52-07NA27344; NNX10AI63G; NNX15AF78G
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
The Astrophysical Journal. Letters
Additional Journal Information:
Journal Volume: 844; Journal Issue: 1; Journal ID: ISSN 2041-8213
Publisher:
Institute of Physics (IOP)
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; 58 GEOSCIENCES; circumstellar matter; meteorites; meteors; meteorides; nucleosynthesis; abundances; stars: AGB and post AGB; stars: carbon; stars: dwarf novae

Citation Formats

Liu, Nan, Stephan, Thomas, Boehnke, Patrick, Nittler, Larry R., Alexander, Conel M. D., Wang, Jianhua, Trappitsch, Reto, Pellin, Michael J., and Davis, Andrew M.. J-type Carbon Stars: A Dominant Source of 14 N-rich Presolar SiC Grains of Type AB. United States: N. p., 2017. Web. doi:10.3847/2041-8213/aa7d4c.
Liu, Nan, Stephan, Thomas, Boehnke, Patrick, Nittler, Larry R., Alexander, Conel M. D., Wang, Jianhua, Trappitsch, Reto, Pellin, Michael J., & Davis, Andrew M.. J-type Carbon Stars: A Dominant Source of 14 N-rich Presolar SiC Grains of Type AB. United States. doi:10.3847/2041-8213/aa7d4c.
Liu, Nan, Stephan, Thomas, Boehnke, Patrick, Nittler, Larry R., Alexander, Conel M. D., Wang, Jianhua, Trappitsch, Reto, Pellin, Michael J., and Davis, Andrew M.. 2017. "J-type Carbon Stars: A Dominant Source of 14 N-rich Presolar SiC Grains of Type AB". United States. doi:10.3847/2041-8213/aa7d4c.
@article{osti_1414353,
title = {J-type Carbon Stars: A Dominant Source of 14 N-rich Presolar SiC Grains of Type AB},
author = {Liu, Nan and Stephan, Thomas and Boehnke, Patrick and Nittler, Larry R. and Alexander, Conel M. D. and Wang, Jianhua and Trappitsch, Reto and Pellin, Michael J. and Davis, Andrew M.},
abstractNote = {Here, we report Mo isotopic data of 27 new presolar SiC grains, including 12 14N-rich AB (14N/15N > 440, AB2) and 15 mainstream (MS) grains, and their correlated Sr and Ba isotope ratios when available. Direct comparison of the data for the MS grains, which came from low-mass asymptotic giant branch (AGB) stars with large s-process isotope enhancements, with the AB2 grain data demonstrates that AB2 grains show near-solar isotopic compositions and lack s-process enhancements. The near-normal Sr, Mo, and Ba isotopic compositions of AB2 grains clearly exclude born-again AGB stars, where the intermediate neutron-capture process (i-process) takes place, as their stellar source. On the other hand, low-mass CO novae and early R- and J-type carbon stars show 13C and 14N excesses but no s-process enhancements and are thus potential stellar sources of AB2 grains. And because both early R-type carbon stars and CO novae are rare objects, the abundant J-type carbon stars (10%–15% of all carbon stars) are thus likely to be a dominant source of AB2 grains.},
doi = {10.3847/2041-8213/aa7d4c},
journal = {The Astrophysical Journal. Letters},
number = 1,
volume = 844,
place = {United States},
year = 2017,
month = 7
}

Journal Article:
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  • We report Mo isotopic data of 27 new presolar SiC grains, including 12 N-14-rich AB (N-14/N-15 > 440, AB2) and 15 mainstream (MS) grains, and their correlated Sr and Ba isotope ratios when available. Direct comparison of the data for the MS grains, which came from low-mass asymptotic giant branch (AGB) stars with large s-process isotope enhancements, with the AB2 grain data demonstrates that AB2 grains show near-solar isotopic compositions and lack s-process enhancements. The near-normal Sr, Mo, and Ba isotopic compositions of AB2 grains clearly exclude born-again AGB stars, where the intermediate neutron-capture process (i-process) takes place, as theirmore » stellar source. On the other hand, low-mass CO novae and early R-and J-type carbon stars show C-13 and N-14 excesses but no s-process enhancements and are thus potential stellar sources of AB2 grains. Because both early R-type carbon stars and CO novae are rare objects, the abundant J-type carbon stars (10%-15% of all carbon stars) are thus likely to be a dominant source of AB2 grains.« less
  • We report Mo isotopic data of 27 new presolar SiC grains, including 12 {sup 14}N-rich AB ({sup 14}N/{sup 15}N > 440, AB2) and 15 mainstream (MS) grains, and their correlated Sr and Ba isotope ratios when available. Direct comparison of the data for the MS grains, which came from low-mass asymptotic giant branch (AGB) stars with large s -process isotope enhancements, with the AB2 grain data demonstrates that AB2 grains show near-solar isotopic compositions and lack s -process enhancements. The near-normal Sr, Mo, and Ba isotopic compositions of AB2 grains clearly exclude born-again AGB stars, where the intermediate neutron-capture processmore » ( i -process) takes place, as their stellar source. On the other hand, low-mass CO novae and early R- and J-type carbon stars show {sup 13}C and {sup 14}N excesses but no s -process enhancements and are thus potential stellar sources of AB2 grains. Because both early R-type carbon stars and CO novae are rare objects, the abundant J-type carbon stars (10%–15% of all carbon stars) are thus likely to be a dominant source of AB2 grains.« less
  • We compared carbon-rich grains with isotopic anomalies to the Sun are found in primitive meteorites. They were made by stars, and carry the original stellar nucleosynthesis signature. Silicon carbide grains of Type X and C and low-density (LD) graphites condensed in the ejecta of core-collapse supernovae. Furthermore, we present a new set of models for the explosive He shell and compare them with the grains showing 12C/ 13C and 14N/ 15N ratios lower than solar. In the stellar progenitor H was ingested into the He shell and not fully destroyed before the explosion. All of the explosion energies and Hmore » concentrations are considered. If the supernova shock hits the He-shell region with some H still present, the models can reproduce the C and N isotopic signatures in C-rich grains. Hot-CNO cycle isotopic signatures are obtained, including a large production of 13C and 15N. The short-lived radionuclides 22Na and 26Al are increased by orders of magnitude. The production of radiogenic 22Ne from the decay of 22Na in the He shell might solve the puzzle of the Ne-E(L) component in LD graphite grains. This scenario is attractive for the SiC grains of type AB with 14N/ 15N ratios lower than solar, and provides an alternative solution for SiC grains originally classified as nova grains. Finally, this process may contribute to the production of 14N and 15N in the Galaxy, helping to produce the 14N/ 15N ratio in the solar system.« less
  • About a year after core-collapse supernova, dust starts to condense in the ejecta. In meteorites, a fraction of C-rich presolar grains (e.g., silicon carbide (SiC) grains of Type-X and low density graphites) are identified as relics of these events, according to the anomalous isotopic abundances. Several features of these abundances remain unexplained and challenge the understanding of core-collapse supernovae explosions and nucleosynthesis. We show, for the first time, that most of the measured C-rich grain abundances can be accounted for in the C-rich material from explosive He burning in core-collapse supernovae with high shock velocities and consequent high temperatures. Themore » inefficiency of the {sup 12}C({alpha}, {gamma}){sup 16}O reaction relative to the rest of the {alpha}-capture chain at T > 3.5 Multiplication-Sign 10{sup 8} K causes the deepest He-shell material to be carbon-rich and silicon-rich, and depleted in oxygen. The isotopic ratio predictions in part of this material, defined here as the C/Si zone, are in agreement with the grain data. The high-temperature explosive conditions that our models reach at the bottom of the He shell can also be representative of the nucleosynthesis in hypernovae or in the high-temperature tail of a distribution of conditions in asymmetric supernovae. Finally, our predictions are consistent with the observation of large {sup 44}Ca/{sup 40}Ca observed in the grains. This is due to the production of {sup 44}Ti together with {sup 40}Ca in the C/Si zone and/or to the strong depletion of {sup 40}Ca by neutron captures.« less
  • Carbon-rich grains with isotopic anomalies compared to the Sun are found in primitive meteorites. They were made by stars, and carry the original stellar nucleosynthesis signature. Silicon carbide grains of Type X and C and low-density (LD) graphites condensed in the ejecta of core-collapse supernovae. We present a new set of models for the explosive He shell and compare them with the grains showing {sup 12}C/{sup 13}C and {sup 14}N/{sup 15}N ratios lower than solar. In the stellar progenitor H was ingested into the He shell and not fully destroyed before the explosion. Different explosion energies and H concentrations aremore » considered. If the supernova shock hits the He-shell region with some H still present, the models can reproduce the C and N isotopic signatures in C-rich grains. Hot-CNO cycle isotopic signatures are obtained, including a large production of {sup 13}C and {sup 15}N. The short-lived radionuclides {sup 22}Na and {sup 26}Al are increased by orders of magnitude. The production of radiogenic {sup 22}Ne from the decay of {sup 22}Na in the He shell might solve the puzzle of the Ne-E(L) component in LD graphite grains. This scenario is attractive for the SiC grains of type AB with {sup 14}N/{sup 15}N ratios lower than solar, and provides an alternative solution for SiC grains originally classified as nova grains. Finally, this process may contribute to the production of {sup 14}N and {sup 15}N in the Galaxy, helping to produce the {sup 14}N/{sup 15}N ratio in the solar system.« less