di Cecco, A.A.di CeccoBecucci, R.R.BecucciBono, G.G.BonoBuonanno, R.R.Buonanno2020-09-172020-09-172010-09-01https://hdl.handle.net/20.500.13025/1992Publications of the Astronomical Society of the Pacific, Volume 122, issue 895, pp.991-999We present precise and deep optical photometry of the globular M92. Data were collected in three different photometric systems Sloan Digital Sky Survey (g ', r ', i ', and z '; MegaCam at CFHT), Johnson-Kron-Cousins ( B , V , and I ; various ground-based telescopes), and Advanced Camera for Surveys (ACS) Vegamag (F475W, F555W, and F814W; Hubble Space Telescope). Special attention was given to the photometric calibration, and the precision of the ground-based data is generally better than 0.01 mag. We computed a new set of alpha-enhanced evolutionary models accounting for the gravitational settling of heavy elements at fixed chemical composition ( [ alpha / Fe ] = + 0.3 , [ Fe / H ] = - 2.32 dex , and Y = 0.248 ). The isochrones-assuming the same true distance modulus ( mu = 14.74 mag ), the same reddening [ E ( B - V ) = 0.025 0.010 mag ], and the same reddening law-account for the stellar distribution along the main sequence and the red giant branch in different color-magnitude diagrams (i ', g ' - i '; i ', and g ' - r '; i ', g ' - z '; I , and B - I ; and F814W and F475W-F814W). The same outcome applies to the comparison between the predicted zero-age horizontal-branch (ZAHB) and the HB stars. We also found a cluster age of 11 1.5 Gyr , in good agreement with previous estimates. The error budget accounts for uncertainties in the input physics and the photometry. To test the possible occurrence of CNO-enhanced stars, we also computed two sets of alpha- and CNO-enhanced (by a factor of 3) models, both at fixed total metallicity ( [ M / H ] = - 2.10 dex ) and at fixed iron abundance. We found that the isochrones based on the former set give the same cluster age ( 11 1.5 Gyr ) as the canonical alpha-enhanced isochrones. The isochrones based on the latter set also give a similar cluster age ( 10 1.5 Gyr ). These findings support previous results concerning the weak sensitivity of cluster isochrones to CNO-enhanced chemical mixtures.Star Clusters and Associations10.1086/656017http://adsabs.harvard.edu/abs/2010PASP..122..991D2010PASP..122..991D