The Naval Observatory Merged Astrometric Dataset (NOMAD)

Abstract

The U.S. Naval Observatory (USNO) announces the release of the first version of the Naval Observatory Merged Astrometric Dataset (NOMAD). The almost 100 GB dataset contains astrometric and photometric data for about 1.1 billion stars derived from the Hipparcos, Tycho-2, UCAC2, Yellow-Blue 6, and USNO-B catalogs for astrometry and optical photometry, supplemented by 2MASS near-infrared photometry. For each unique star the ”best” astrometric and photometric data are chosen from the source catalogs and merged into a single dataset. A sequence of priorities is followed and NOMAD contains flags to identify the source catalogs and gives cross-reference identifications. This first release of NOMAD is not a compiled catalog; that is, if a star is identified in more than 1 of the above mentioned catalogs, only 1 catalog entry is chosen. Thus the local and global systematic errors of the various source catalogs will be present in this version of NOMAD. All source catalogs astrometric data are on the International Celestial Reference System within the limitations of the source catalogs. For more information and data retrieval see our homepage www.nofs.navy.mil/nomad. Here is a screen capture of the NOMAD web interface. Sample Data Across the bottom of this poster paper a sample of the NOMAD catalog output for a field at α = 0 and δ = 0◦ is given. The data are retrieved from the web interface.