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Session 4 - The Sun.
Display session, Monday, June 09
South Main Hall,

[4.01] A Re-evaluation of the Abundance of Lutetium in the Sun

D. J. Bord (UMich-Dbn), C. R. Cowley (UMich), D. Mirijanian (UMich-Dbn)

Reasonable photospheric abundances have been determined for 12 of the 14 lanthanide rare earth elements. Disagreements with CI chondritic abundances exceed 0.3 dex for only two species: Tb and Lu. This paper concerns the latter element, for which the solar determination is 0.63 dex above the meteoritic value.

Grevesse and Blanquet (Solar Physics 9, 5, 1969) determined the solar Lu abundance from a single line at \lambda_ødot3397.062. Andersen, et al. (Solar Physics \bf44, 257, 1975) made a small revision in the value based on new lifetime measurements. The feature identified as Lu II is in the wing of a stronger Fe I line at \lambda_ødot3396.981, but this line is not the cause of the discordant abundance. An equivalent width can certainly be estimated to within 50% or so. We measured 27 mÅvery close to the value given in NBS Monograph 61.

It has been suggested that the 3997.062 feature is itself a blend, with only a minor contribution from Lu II. We find that this is most probably the case. The dominant contributor to the feature is a line of NH predicted by Kurucz from molecular constants to be at \lambda3397.078.

We have calculated oscillator strengths for Lu II and have synthesized a 5 Åregion of the solar spectrum centered on the \lambda3397 feature. While overall uncertainties in the calculation of both the atomic and molecular features are surely a factor of two, based on the fit between the computed and the observed spectrum, we find no compelling reason to believe that the solar lutetium abundance departs significantly from that of the CI meteorites. Log(gf) values for additional strong lines in the optical spectrum of Lu II will be reported.

We thank N. Grevesse and A. Sauval for the digitized version of the solar spectrum used in the analysis.

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