[Previous] | [Session 57] | [Next]
L. J. Hainline (Caltech), C. P. Deliyannis, S. Margheim (Indiana U.)
Robichon et al. (2000) have indicated that the Hipparcos Pleiades distance problem goes away if the metallicity of the Pleiades is [Fe/H]=-0.11+/-0.025, and that of the Praesepe is +0.17+/-0.01 (which is slightly more metal-rich than generally accepted values for the Hyades). Using, a) new U-B, U-V, U-R, and U-I, vs. B-V color-color calibrations based on Johnson and Mendoza UBVRI photometry of the Hyades, and on the metallicity dependence from Yale-Yonsei 2001 isochrones, b) Johnson and Mendoza photometry of other clusters, and c) high resolution spectroscopic studies by Boesgaard and collaborators, we examine whether the metallicities quoted by Robichon are tenable. We find that, a) almost independently of the Johnson-Mendoza photometry, the Boesgaard cluster results differ markedly from those quoted by Robichon, and particularly her results imply Praesepe-Pleiades<0.1dex, not =0.28dex as required by Robichon; our own analysis using Boesgaard's equivalent widths confirms her rankings, b) the color-color diagrams, alone, show that Praesepe is more metal-poor, not more metal-rich, than the Hyades, and c) the color-color diagrams, alone, support the combination [Fe/H]=0.0 and E(B-V)=0.04 for the Pleiades, as espoused by Boesgaard, and not the combination [Fe/H]=-0.11 and E(B-V)=0.04, as espoused by Robichon. The derived spectroscopic abundances using Fe I lines depend on Teff, which depends on [Fe/H] and choice of E(B-V). Using Boesgaard's equivalent widths for the Pleiades, we explore the intriguing possibility that E(B-V)=0.00 implies [Fe/H]=-0.10; however, the reddening derived from the photometry depends on the adopted cluster metallicity, and we find that [Fe/H]=-0.10 is inconsistent with E(B-V)=0.00. Carrying this argument through to its logical conclusion by iterating E (and [Fe/H]) --> Teff --> [Fe/H] --> E --> Teff --> [Fe/H] ..., we converge on the combination of E=0.04 and [Fe/H] = 0.00. Thus, simultaneous consideration of the Boesgaard spectroscopy and Johnson-Mendoza photometry leads to the same conclusion. The Hipparcos Pleiades distance problem remains unresolved. This work has been supported by the National Science Foundation under Grant AST-9812735.