MAST hosts a copy of the SkyMapper DR4 catalog. SMSS DR4 contains optical photometry in the 6 SkyMapper filters (u,v,g,r,i,z) for ~700 million astrophysical sources over 26,000 sq.deg, ranging from the South Celestial Pole to Dec=+16 degrees for objects with data in all bands, and some sources as far North as +29 degrees. The photometry is drawn from over 15 billion measurements made from more than 400,000 images acquired by the 1.3m SkyMapper telescope between March 2014 and September 2021. The typical 10-sigma depths for each field range between 18.5 and 20.5 ABmag, depending on the filter, but certain sky regions include longer exposures that reach as deep as 22 ABmag. Compared to previous SkyMapper data releases, DR4 includes significant enhancements in data processing, most notably a new photometric calibration anchored to synthetic photometry from Gaia low-resolution spectroscopy, which resolves reddening- and spatial-trends identified in previous releases, especially in the bluest filters, u and v. A large number of other photometric and spectroscopic surveys have been cross-matched to the dr4.master table of objects, to facilitate various scientific investigations.

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