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The High Resolution Fly's Eye (HiRes) experiment has observed the Greisen-Zatsepin-Kuzmin suppression (called the GZK cutoff) with a statistical significance of five standard deviations. HiRes' measurement of the flux of ultrahigh energy cosmic rays shows a sharp suppression at an energy of 6 x 10(19) eV, consistent with the expected cutoff energy. We observe the ankle of the cosmic-ray energy spectrum as well, at an energy of 4 x 10(18) eV. We describe the experiment, data collection, and analysis and estimate the systematic uncertainties. The results are presented and the calculation of the statistical significance of our observation is described.

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We present an optical and near-infrared study of a 45 0 Â 45 0 field in NGC 2264, which includes both S Mon and the Cone Nebula. We report photometry at optical (UBVR C I C ) and near-infrared (JHK) wavelengths for $5600 stars and spectroscopic classifications for $400 of these stars. We identify circumstellar disk candidates using three techniques: excess ultraviolet (UÀV ) emission, excess near-IR (IÀK and HÀK) emission, and H emission-line equivalent widths for those stars with spectra. We find generally good correlation between disk indicators thought to originate from different physical processes. We find little if any evolution of disk fraction with stellar age or mass. However, when we derive mass accretion rates ( _ M M) from the excess emission at U, we find that _ M M decreases with age over the age range spanned by our data, $0.1-5 Myr, and increases with mass over the range $0.25-1 M . These findings are comparable to results found previously by us in the Orion Nebula cluster flanking fields.