Metallicity mapping with gri photometry: The virgo overdensity and the halos of the galaxy

Timothy C. Beers, Deokkeun An, Jennifer A. Johnson, Marc H. Pinsonneault, Donald M. Terndrup, Franck Delahaye, Young Sun Lee, Thomas Masseron, Daniela Carollo, Brian Yanny

    Research output: Contribution to journalArticlepeer-review


    We describe the methodology required for estimation of photometric estimates of metallicity based on the SDSS gri passbands, which can be used to probe the properties of main-sequence stars beyond ∼10 kpc, complementing studies of nearby stars from more metallicity-sensitive color indices that involve the u passband. As a first application of this approach, we determine photometric metal abundance estimates for individual main-sequence stars in the Virgo Overdensity, which covers almost 1000 deg2 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, internal errors of σ[Fe/H] ∼0.1 dex can be achieved for bulk stellar populations. The global metal abundance of the Virgo Overdensity determined in this way is 〈[Fe/H]〉 = -2.0±0.1 (internal) ±0.5 (systematic), from photometric measurements of 0.7 million stars with heliocentric distances from ∼10 kpc to ∼20 kpc. A preliminary metallicity map, based on results for 2.9 million stars in the northern SDSS DR-7 footprint, exhibits a shift to lower metallicities as one proceeds from the inner- to the outer-halo population, consistent with recent interpretation of the kinematics of local samples of stars with spectroscopically available metallicity estimates and full space motions.

    Original languageEnglish
    Pages (from-to)127-130
    Number of pages4
    JournalProceedings of the International Astronomical Union
    Issue numberS262
    Publication statusPublished - Aug 2009


    • Astronomical data bases: surveys
    • Galaxy: halo
    • Methods: data analysis
    • Stars: abundances
    • Structure


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