Parsec-scale Variations in the 7Li/6Li Isotope Ratio Toward IC 348 and the Per OB 2 Association

TL;DR

This study investigates variations in the lithium isotope ratio in the interstellar medium near IC 348, revealing cosmic-ray-induced lithium production and linking it to a surrounding superbubble.

Contribution

It provides new measurements of lithium isotopic ratios near IC 348, demonstrating cosmic-ray influence and associating superbubbles with isotope variations.

Findings

7Li/6Li ratio near o Per is about 2, indicating cosmic-ray spallation.

Confirmed cosmic-ray production of lithium in the vicinity of IC 348.

Superbubble surrounding IC 348 likely source of cosmic rays affecting isotope ratios.

Abstract

Measurements of the lithium isotopic ratio in the diffuse interstellar medium from high-resolution spectra of the LiI {\lambda}6708 resonance doublet have now been reported for a number of lines of sight. The majority of the results for the 7Li/6Li ratio are similar to the Solar System ratio of 12.2 but the line of sight toward o Per, a star near the star-forming region IC 348, gave a ratio of about 2, the expected value for gas exposed to spallation and fusion reactions driven by cosmic rays. To examine the association of IC 348 with cosmic rays more closely, we measured the lithium isotopic ratio for lines of sight to three stars within a few parsecs of o Per. One star, HD 281159, has 7Li/6Li ~ 2 confirming production by cosmic rays. The lithium isotopic ratio toward o Per and HD 281159 together with published analyses of the chemistry of interstellar diatomic molecules suggest that the superbubble surrounding IC 348 is the source of the cosmic rays.