in GC age determinations. They estimate the age of the oldest Galactic GCs using the main-sequence turn-off luminosity and evaluate the errors with Monte-Carlo techniques, paying careful attention to uncertainties in the distance, to systematics, and to model uncertainties. They find a best-fit age for the oldest Galactic GCs of $12.5^{+3.4}_{-2.2}$ Gyr (95% confidence limits). We adopt their probability distribution for the oldest GC age, which we find can be accurately described by $$P(t)=\frac{A}{\sigma (t-T)} \exp \left[- \frac{\ln \left[ (t-T)/m \right
]^2}{2 \sigma^2} \right ]
\label{eq:kraussagecorr}$$ where $t$ denotes the age of the oldest GCs, $A=1.466$, $\sigma=0.25$, $T=6.5$ and $m=5.9$. Since reionization took place at $z\sim 17$ [@KogutWMAP03] and we assume that oldest GCs must have formed before then, for all reasonable cosmologies we only need add $0.2-0.3$ Gyr to the GC ages to obtain an estimate of the age of the universe. We conservatively add 0.3 Gyr[^2].

In order to constrain $w$, we assume a flat universe and Monte Carlo simulate the distribution of $\ell_1$ subject to only weak constraints on the other cosmological parameters. For different values of $w$, we generate $10^5$ models, randomly sampling the cosmological parameters $\Omega_m$, $\Omega_bh^2$ and $h$ with uniform priors, $0.5< h < 