The interstellar ^7^Li/^6^Li ratio. The line of sight to ζ Ophiuchi.

Details The interstellar ^7^Li/^6^Li ratio. The line of sight to ζ Ophiuchi. The interstellar ^7^Li/^6^Li ratio. The line of sight to ζ Ophiuchi.

Jun 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995a%26a...298..879l&link_type=abstract

Astronomy and Astrophysics, v.298, p.879

Astronomy and Astrophysics

Astrophysics

35

Ism: Atoms, Ism: Abundances, Galaxy: Abundances, Nucleosynthesis

Scientific paper

We report our observations of the λ6708A absorption lines of interstellar ^6^LiI and ^7^LiI in the direction of ζ Oph, conducted at the ESO 3.6m Telescope linked via fibre optics to the Echelle Coude Spectrometer. Our LiI data revealed after a careful reduction to be of a higher quality than those previously obtained on the same line of sight, with a resolving power λ/{DELTA}λ=100000 and a signal-to-noise ratio S/N=7500 per pixel. We detect one main A and one weak B absorbing interstellar components in both LiI and KI spectra. Using sophisticated profile fitting techniques, we are able to derive two isotopic ratios, (^7^Li/^6^Li)_A_=8.6+/-0.8(+/-1.4 systematics), and (^7^Li/^6^Li)_B_=1.4^+1.2^_-0.5_(+/-0.6 systematics). We show that the results of Meyer et al. (1993) for the ^7^Li/^6^Li ratio toward ζ Oph, ^7^Li/^6^Li=6.8^+1.4^_-1.7_, and toward ζ Per for similar reasons ^7^Li/^6^Li=5.5^+1.3^_-1.1_, are biased because only one interstellar component was taken into account in their analysis whereas two at least are clearly present. As well, we find that an average value of the ^7^Li/^6^Li ratio on the line of sight to ζ Oph should lie closer to 8-9 than to 6-7. The ratio derived by Ferlet & Dennefeld (1984) toward ζ Oph is unexplained, ^7^Li/^6^Li>25, eventhough ^6^Li was not detected for that time. The (^7^Li/^6^Li)_A_ ratio derived here is in slight agreement with the ^7^Li/^6^Li ratio measured toward ρ Oph, ^7^Li/^6^Li=11.1+/-2, and strongly argues for the existence of an extra source of ^7^Li in the Galaxy. The (^7^Li/^6^Li)_B_ ratio is not readily explained either by an instrumental contamination, by the presence of additional clouds on the line of sight, or even by a massive interaction of cosmic rays with the material of cloud B. Although none of these hypotheses seems entirely satisfactory, each one of them implies that the value derived in cloud A should be higher than what is observed, i.e. (^7^Li/^6^Li)_A_>8.6.

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