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We have constrained the age of the globular cluster S312 in the Andromedagalaxy (M31) by comparing its multicolor photometry with theoretical stellarpopulation synthesis models. This is both a check on the age of this globularcluster, as well a check on our methodology. Main-sequence photometry has beenthe most direct method for determining the age of a star cluster. S312 wasobserved as part of the Beijing-Arizona-Taiwan-Connecticut (BATC) MulticolorSky Survey from 1995 February to 2003 December. The photometry of BATC imagesfor S312 was taken with 9 intermediate-band filters covering 5000-10000\AA.Combined with photometry in the near-ultraviolet (NUV) of {\sl GALEX},broad-band $UBVR$ and infrared $JHK_s$ of 2MASS, we obtained the accuratespectral energy distributions (SEDs) of S312 from 2267-20000\AA. A quantitativecomparison to simple stellar population models yields an age of$9.5_{-0.99}^{+1.15}$ Gyr, which is in very good agreement with the previousdetermination by main-sequence photometry. S312 has a mass of$9.8\pm{1.85}\times 10^5 \rm M_\odot$, and is a medium-mass globular cluster inM31. By analysis of errors of ages determined based on the SED fitting methodof this paper, secure age constraints are derived with errors of $< 3$ Gyr forages younger than 9 Gyr. In fact, the theoretical SEDs are not sensitive to thevariation of age for ages greater than $\sim 10$ Gyr. Therefore, for globularclusters as old as the majority of the Galactic GCs, our method do notdistinguish them accurately. We emphasize that our results show that even withmultiband photometry spanning NUV to $K_s$, our age constraints from SEDfitting are distressingly uncertain, which has implications for age derivationsin extragalactic globular cluster systems.Comment: Accepted for Publication in ApJ, 9 pages, 5 figure

Age Constraints for an M31 Globular Cluster from SEDs Fit