ON THE METALLICITY AND THE TURNOFF TEMPERATURE OF M67

High-dispersion echelle spectra of five stars located along the main sequence of M67 are analyzed, using the model atmospheres of Kurucz. An average iron abundance of the cluster, relative to the Sun, of [Fe/H] = -0.04 +/- 0.12 is derived from the observed equivalent widths of up to four weak Fe II lines in each of the five spectra and in the solar spectrum. With this known relative iron abundance, the equivalent widths of up to six Fe I lines in these same spectra then require that the effective temperatures of the two brightest, hottest program stars average <T(e)>2 = 6165 +/- 60 K. This average temperature approximates satisfactorily the upper limit on the temperatures actually reached in the turnoff region. The uncertain Fe II oscillator strengths were calibrated by requiring that, for the physically very similar Sun, the identical analysis recover the correct effective temperature from the same Fe II and Fe I lines. Finally, a turnoff age of tau = 5.2 +/- 1.0 Gyr is derived by comparing the limiting turnoff temperature <T(e)>2 to appropriate isochrones in the theoretical H-R diagram, as calculated by VandenBerg (1990, private communication). A primary advantage of this purely spectroscopic method is that it effectively requires no estimates of the reddening or the intrinsic colors of the clusters stars or of the distance to the cluster; the attendant uncertainties in these cluster parameters are thereby circumvented entirely.