An Ultra-high-Resolution Survey of the Interstellar 7Li/6Li Isotope Ratio in the Solar Neighborhood
Abstract
In an effort to probe the extent of variations in the interstellar 7Li/6Li ratio seen previously, ultra-high-resolution (R~360,000), high signal-to-noise spectra of stars in the Perseus OB2 and Scorpius OB2 associations were obtained. These measurements confirm our earlier findings of an interstellar 7Li/6Li ratio of about 2 toward ο Per, the value predicted from models of Galactic cosmic-ray spallation reactions. Observations of other nearby stars yield limits consistent with the isotopic ratio of ~12 seen in carbonaceous chondrite meteorites. If this ratio originally represented the gas toward ο Per, then to decrease the original isotope ratio to its current value an order of magnitude increase in the Li abundance is expected, but it is not seen. The elemental K/Li ratio is not unusual, although Li and K are formed via different nucleosynthetic pathways. Several proposals to account for the low 7Li/6Li ratio were considered, but none seems satisfactory. Analysis of the Li and K abundances from our survey highlighted two sight lines where depletion effects are prevalent. There is evidence for enhanced depletion toward X Per, since both abundances are lower by a factor of 4 when compared to other sight lines. Moreover, a smaller Li/H abundance is observed toward 20 Aql, but the K/H abundance is normal, suggesting enhanced Li depletion (relative to K) in this direction. Our results suggest that the 7Li/6Li ratio has not changed significantly during the last 4.5 billion years and that a ratio of ~12 represents most gas in the solar neighborhood. In addition, there appears to be a constant stellar contribution of 7Li, indicating that one or two processes dominate its production in the Galaxy.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- March 2003
- DOI:
- 10.1086/346264
- arXiv:
- arXiv:astro-ph/0212233
- Bibcode:
- 2003ApJ...586..268K
- Keywords:
-
- ISM: Abundances;
- ISM: Atoms;
- Galaxy: Open Clusters and Associations: Individual: Name: Perseus OB2;
- Galaxy: Open Clusters and Associations: Individual: Name: Scorpius OB2;
- Galaxy: Solar Neighborhood;
- Stars: Individual: Constellation Name: 20 Aquilae;
- Stars: Individual: Constellation Name: ζ Ophiuchi;
- Stars: Individual: Constellation Name: χ Ophiuchi;
- Stars: Individual: Constellation Name: ο Persei;
- Stars: Individual: Constellation Name: X Persei;
- Astrophysics
- E-Print:
- 54 pages, accepted for publication in the Astrophysical Journal