The age of the galaxy from thorium in G dwarfs, a re-analysis.

Detailed model atmospheres and synthetic spectra have been used in a re-analysis of the Butcher (1987) data for the thorium and neodymium abundances of 20 solar-type stars (including two new, low-metallicity stars), with different ages and over-all metal abundances. New, very accurate laboratory wavelengths have been used for the principle lines in the synthetic spectrum analyses. We suspect the presence of a spectral line at about 4019.10 A, very close to the thorium line used for the analysis, and not included in any previous investigation. This line may be a major contributor to the large scatter in our final results, but unfortunately no identification has been possible. It has also been found that the cobalt line at 4019.126 A shows hyperfine structure, and this has been taken into account in the analysis. The major trend previously found in this sample by Butcher is confirmed, but the large scatter prevents us from drawing any firm conclusions concerning the age of the Galaxy.