Statistics and supermetallicity: The metallicity of NGC 6791
Astronomy and Astrophysics
For the old galactic cluster NGC 6791, Peterson & Green (1998a) and Chaboyer et al. (1999) have found that [Fe/H] ∼ +0.4 dex. A second look at that conclusion is taken in this paper. Zero-point problems are reviewed for a high-dispersion analysis done by Peterson & Green, and it is found that accidental errors have not been determined rigorously for the results of that analysis. It is also noted that in a color-magnitude analysis performed by Chaboyer et al., the important metallicity range
... tallicity range between 0.0 and +0.3 dex is not explored and hence is not ruled out. Moreover, that analysis does not yield statistically rigorous results, and it appears that such results may not be produced in color-magnitude analysis of clusters in general. Results in the two cited papers and elsewhere are re-evaluated statistically, with an allowance being made for uncertainty in the cluster reddening. Apparently the best that can be said at present is that the cluster metallicity lies in the range from +0.16 to +0.44 dex. This conclusion is stressed by reviewing the immaturity of the underlying data base. The premature conclusion for a high metallicity turns out to be due largely to neglect of accidental errors, though a tendency to ascribe too much weight to high derived metallicities may also play a role.