A PHOTOMETRIC METALLICITY ESTIMATE OF THE VIRGO STELLAR OVERDENSITY

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 +/- 0.1 (internal) +/- 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 similar to 10 kpc to similar to 20 kpc. The metallicity of the VOD is indistinguishable, within Delta[Fe/H] <= 0.2, from that of field halo stars covering the same distance range. This initial application suggests that the Sloan Digital Sky Survey gri passbands can be used to probe the properties of main-sequence stars beyond similar to 10 kpc, complementing studies of nearby stars from more metallicity-sensitive color indices that involve the u passband.