Nitrogen Isotopes in Asymptotic Giant Branch Carbon Stars and Presolar SiC Grains: A Challenge for Stellar Nucleosynthesis
Abstract
Isotopic ratios of C, N, Si, and trace heavy elements in presolar SiC grains from meteorites provide crucial constraints to nucleosynthesis. A long-debated issue is the origin of the so-called A+B grains, as of yet no stellar progenitor thus far has been clearly identified on observational grounds. We report the first spectroscopic measurements of 14N/15N ratios in Galactic carbon stars of different spectral types and show that J- and some SC-type stars might produce A+B grains, even for 15N enrichments previously attributed to novae. We also show that most mainstream grains are compatible with the composition of N-type stars, but in some cases might also descend from SC stars. From a theoretical point of view, no astrophysical scenario can explain the C and N isotopic ratios of SC-, J-, and N-type carbon stars together, as well as those of many grains produced by them. This poses urgent questions to stellar physics.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- May 2013
- DOI:
- 10.1088/2041-8205/768/1/L11
- arXiv:
- arXiv:1303.6418
- Bibcode:
- 2013ApJ...768L..11H
- Keywords:
-
- nuclear reactions;
- nucleosynthesis;
- abundances;
- stars: carbon;
- stars: abundances;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- 2 figures, 21 pages, Accepted in Astrophysical Journal Letters