2007ApJ...659..359M

We have constrained the age of the globular cluster S312 in the Andromeda galaxy (M31) by comparing its multicolor photometry with theoretical stellar population synthesis models. This is both a check on the age of this globular cluster and a check on our methodology. Main-sequence photometry has been the most direct method for determining the age of a star cluster. S312 was observed as part of the Beijing-Arizona-Taiwan-Connecticut (BATC) Multicolor Sky Survey from 1995 February to 2003 December. The photometry of BATC images for S312 was taken with nine intermediate-band filters covering 5000-10000 Å. Combined with photometry in the near-ultraviolet (NUV) of GALEX, broadband UBVR, and infrared JHK_sof 2MASS, we obtained the accurate spectral energy distributions (SEDs) of S312 from 2267-20000 Å. A quantitative comparison to simple stellar population models yields an age of 9.5^+1.15_–0.99 Gyr, which is in very good agreement with the previous determination by main-sequence photometry. S312 has a mass of 9.8±1.85x10⁵ M_☉and is a medium-mass globular cluster in M31. By analyzing the errors of ages determined based on the SED-fitting method of this paper, secure age constraints are derived with errors of <3 Gyr for ages younger than 9 Gyr. In fact, the theoretical SEDs are not sensitive to the variation of age for ages > ∼10 Gyr. Therefore, our method does not accurately distinguish globular clusters (GCs) as old as the majority of the Galactic GCs. We emphasize that our results show that even with multiband photometry spanning from NUV to K_s, our age constraints from SED fitting are distressingly uncertain, which has implications for age derivations in extragalactic globular cluster systems.