Note: Note that the errors on the proper motions are large (∼50mas/yr), and therefore the positions computed at an epoch different from 1991.25 have a large (∼0.4") uncertainty. The Tycho Epoch Photometry data can be accessed from the morePhoto column (includes VT, BT and Hp photometric data for Hipparcos stars [filter responses]
Note: USNO-A2.0 contains 526,280,881 sources, and is based on a re-reduction of the Precision Measuring Machine (PMM) scans from POSS-I O and E plates (>=-18°) and SRC-J and ESO-R plates (<=-20°). USNO-A2.0 was created by Dave Monet () and collaborators at Flagstaff Station, U.S. Naval Observatory. The major difference between USNO-A2.0 and its previous version USNO-A1.0 is that A1.0 used the Guide Star Catalog as its reference frame whereas A2.0 uses the ICRF as realized by the USNO ACT catalog (Urban et al. 1997). The VizieR search engine uses an on-line compressed version (3.6Gbytes) which was generated at CDS.
Note: The Guide Star Catalog has been constructed to support the operational need of the Hubble Space Telescope. It contains over 25 million positions for about 19 million objects, of which more than 15 million are classified as stars. The version 1.2 is a new astrometric reduction which results in absolute position errors about 0.3-0.4 arcsec. (see GSC pages at URL http://www-gsss.stsci.edu/gsc/gsc.html)
Note: The GSC-ACT (or GSC1.3) is a recalibration of the GSC1.1, the catalogue constructed to support the operational need of the Hubble Space Telescope, with the ACT, the combination of the Astrographic Catalogue and the Tycho catalogue derived from the Hipparcos mission; see http://www.projectpluto.com/gsc_act.htm for more details about this recalibration.
Note: The construction of the GSC-II is still in progress: this version has no proper motions, and the magnitude limits are 18.5 in F (red) and 19.5 in J (blue). The data are copyrighted, check the data use Policy.
Note: the J2000 coordinates are not part of the original catalogue; their accuracy can be low, see the CooFlag column
Note: Detailed introduction can be found in intro.tex (see also http://aries.usno.navy.mil/ad/ac.html) Direct links to Hipparcos and Tycho observations are provided from the relevant columns.
Note: The USNO-B Catalog presents positions, proper motions, magnitudes un blue, red and infrared, as well as star/galaxy estimators for 1,045,175,762 objects derived from 3,648,832,040 separate observations. The data were taken from scans of 7,435 Schmidt plates taken from various sky surveys during the last 50 years. USNO-B1.0 catalog was created by Dave Monet and collaborators at http://www.nofs.navy.mil/data/fchpix/ Note that the star/galaxy estimators may be mixed up in dense regions.
Note: The Naval Observatory Merged Astrometric Dataset (NOMAD) contains astrometric and photometric data for over 1 billion stars derived from the Hipparcos (I/239), Tycho-2 (I/259), UCAC2 (I/289), and USNO-B1.0 (I/284) catalogs for astrometry and optical photometry, supplemented by 2MASS (II/246) near-infrared photometry. An efficient remote query program findnomad1 is available in the cdsclient package, for Unix/Linux platforms
Note: This version of the GSC-II has no proper motions, but the limits on brightness which existed on GSC2.2 (F<18.5, Bj<19.5) were removed.
Note: The limiting magnitude is about 15.2 in the GSC photometric system.
Note:
Note: see the UCAC4 document, and the the fix for high proper motion stars. The UCAC home page is available at http://www.usno.navy.mil/USNO/astrometry/optical-IR-prod/ucac. Please acknowledge the usage of the UCAC4
(original column names in green) (1692919135 rows)
(original column names in green) (1811709771 rows)
