We present our analysis of archival Hubble Space Telescope Wide Field Planetary Camera 2 observations in F555W ( \sim V ) and F450W ( \sim B ) of the intermediate-age populous star cluster NGC 416 in the Small Magellanic Cloud galaxy .
We use published photometry of two other SMC populous star clusters , Lindsay 1 and Lindsay 113 , to investigate the age sequence of these three star clusters .
We estimate that these clusters have age ratios of age _ { NGC 416 } / age _ { L 1 } \approx 0.73 \pm 0.05 and age _ { L 113 } / age _ { L 1 } \approx 0.52 \pm 0.09 using an extrapolation of the d _ { ( B - V ) } method ( which uses the color difference between the red horizontal branch and the red giant branch as an age indicator ) of Sarajedini , Lee , & Lee [ ApJ , 450 , 712 ( 1995 ) ] .
These age ratios provide absolute age estimates of 6.6 \pm 0.5 Gyr and 4.7 \pm 0.8 Gyr for NGC 416 and Lindsay 113 , respectively , assuming that Lindsay 1 is 9 Gyr old .
Metallicities of \hbox { [ Fe / H ] } = -1.44 \pm 0.12 , -1.35 \pm 0.08 , -1.24 \pm 0.11 dex , and reddenings of \hbox { E$ ( \hbox { $B - V$ } ) $ } = 0.08 \pm 0.03 , 0.06 \pm 0.02 , 0.00 \pm 0.02 mag for NGC 416 , Lindsay 1 , and Lindsay 113 , respectively , were determined using the simultaneous reddening and metallicity ( SRM ) method of Sarajedini & Layden [ AJ , 113 , 264 , ( 1997 ) ] .
Accurate ( relative ) ages for the intermediate-age populous clusters in the Small Magellanic Cloud ( e.g .
via deep main sequence photometry ) would allow the d _ { ( B - V ) } method to be recalibrated with star clusters that are significantly younger than 7 Gyr .
An extended d _ { ( B - V ) } method could prove to be a very useful age diagnostic for future studies of the intermediate-age metal-poor stellar populations in Local Group galaxies where accurate main-sequence turnoff photometry at M _ { V } \approx +4 mag is currently not possible or practical .