Abstract
The results of observing 118 subdwarfs and a number of Hyades stars with a 13-color medium-narrow-band photometric system are examined. Blanketing curves are constructed by comparing the subdwarf photometry to mean Hyades colors at constant effective temperature. For the temperature range of F, G, and early-K main sequence stars, the 13-color indices give a clear separation between the effects of temperature, metallicity, and surface gravity: 0.45-0.63 (microns) and 0.58-0.99 are good for measuring temperature, 0.37-0.45 is very sensitive to metallicity, and G equals (0.35-0.52)-(0.37-0.45) is a good gravity index. It is shown that the cooler evolving subdwarfs indicate that the extreme Population II objects formed over a time interval of at least 2 x 10 to the 9th years. Finally, the cosmological implications of such a range in subdwarf ages are discussed.
