We determine photometric metal abundance estimates for individual main-sequence stars in the Virgo Overdensity ( VOD ) , which covers almost 1000 \deg ^ { 2 } on the sky , based on a calibration of the metallicity sensitivity of stellar isochrones in the gri filter passbands using field stars with well-determined spectroscopic metal abundances .
Despite the low precision of the method for individual stars , we derive { [ Fe / H ] } = -2.0 \pm 0.1 { ( internal ) } \pm 0.5 { ( systematic ) } for the metal abundance of the VOD from photometric measurements of 0.7 million stars in the Northern Galactic hemisphere with heliocentric distances from \sim 10 kpc to \sim 20 kpc .
The metallicity of the VOD is indistinguishable , within \Delta { [ Fe / H ] } \leq 0.2 , from that of field halo stars covering the same distance range .
This initial application suggests that the SDSS gri passbands can be used to probe the properties of main-sequence stars beyond \sim 10 kpc , complementing studies of nearby stars from more metallicity-sensitive color indices that involve the u passband .