United States Naval Observatory, Flagstaff Station
Description:
USNO-A2.0 is a catalog of 526,280,881 stars, and is based on a re-reduction of the Precision Measuring Machine (PMM) scans that were the basis for the USNO-A1.0 catalog. The major difference between A2.0 and A1.0 is that A1.0 used the Guide Star Catalog (Lasker et al. 1986, see Cat. <I/220>) as its reference frame whereas A2.0 uses the ICRF as realized by the USNO ACT catalog (Urban et al. 1997, see Cat. II/246>). A2.0 presents right ascension and declination (J2000, epoch of the mean of the blue and red plate) and the blue and red magnitude for each star. Usage of the ACT catalog as well as usage of new astrometric and photometric reduction algorithms should provide improved astrometry (mostly in the reduction of systematic errors) and improved photometry (because the brightest stars on each plate had B and V magnitudes measured by the Tycho experiment on the Hipparcos satellite). The basic format of the catalog and its compilation is the same as for A1.0, and most users should be able to migrate to this newer version with minimal effort. (1 data file).
Sternberg Astronomical Institute Virtual Observatory Project
Description:
USNO-A2.0 is a catalog of 526,280,881 stars, and is
based on a re-reduction of the Precision Measuring Machine (PMM) scans
that were the basis for the USNO-A1.0 catalog. The major difference between
A2.0 and A1.0 is that A1.0 used the Guide Star Catalog (Lasker et al. 1986,
as its reference frame whereas A2.0 uses the ICRF as realized by the USNO
ACT catalog (Urban et al. 1997).
USNO-B is an all-sky catalog that presents positions, proper motions, magnitudes in various optical
passbands, and star/galaxy estimators for 1,042,618,261 objects derived from 3,643,201,733 separate
observations. The data were obtained from scans of 7435 Schmidt plates taken for the various sky surveys
during the last 50 years. USNO-B1.0 is believed to provide all-sky coverage, completeness down to V = 21,
0>2 astrometric accuracy at J2000, 0.3 mag photometric accuracy in up to five colors, and 85% accuracy for
distinguishing stars from nonstellar objects.
A more detailed description of the construction and contents of the USNO-B1 catalog can be found in Monet et al.
(2003, "The USNO-B Catalog", AJ, 125, 984), http://www.usno.navy.mil/USNO/astrometry/optical-IR-prod/usno-b1.0/resolveuid/41be0c1a4d1a8372289bad3baf27cde5.
A mirror of USNOB exists in the MAST holdings and is thus available as a cone search.
All available catalogs are listed at http://archive.stsci.edu/vo/mast_services.html.
United States Naval Observatory, Flagstaff Station
Description:
USNO-B is an all-sky catalog that presents positions, proper motions, magnitudes in various optical passbands, and star/galaxy estimators for 1,042,618,261 objects derived from 3,643,201,733 separate observations. The data were obtained from scans of 7435 Schmidt plates taken for the various sky surveys during the last 50 years. USNO-B1.0 is believed to provide all-sky coverage, completeness down to V=21, 0.2" astrometric accuracy at J2000, 0.3 mag photometric accuracy in up to five colors, and 85% accuracy for distinguishing stars from nonstellar objects. A brief discussion of various issues is given here, but the actual data are available from the US Naval Observatory Web site and others.
This table contains the metadata for the plates that went into USNO-B
1.0 as best as we can reconstruct it (i.e., largely those that also
make up the Digital Sky Survey DSS). Most of the source files were
obtained from http://www.nofs.navy.mil/data/fchpix/, some additional
contributions came from Dave Monet.
Accurate positional measurements of planets and satellites are used to improve their orbits, our knowledge of their dynamics and to infer the accuracy of the planet and satellite ephemerides. In the framework of the European FP7 ESPaCE program, we provide the positions of Mars, Phobos, and Deimos taken with the U.S. Naval Observatory 61-inch astrometric reflector and 26-inch refractor from 1967 to 1997. 425 astrophotographic plates were measured with the digitizer of the Royal Observatory of Belgium and reduced through an optimal process which includes image, instrumental, and spherical corrections using the UCAC4 catalog to provide the most accurate equatorial (RA, DEC) positions.
The U.S. Naval Observatory CCD trigonometric parallax program is described in detail, including the instrumentation employed, observing procedures followed, and reduction procedures applied. Astrometric results are presented for 72 stars ranging in apparent brightness from V=15.16 to 19.58. Photometry (V and V-I on the Kron-Cousins system) is presented for the parallax stars and for all 426 individual reference stars employed in the astrometric solutions. Corrections for differential color refraction, calibrated to the observed V-I colors, have been applied to all astrometric measures. The mean errors in the relative parallaxes range from +/-0.0005" to +/-0.0027" with a median value of +/-0.0010". Seventeen of the 23 stars with V_tan_>200km/s form a well-delineated sequence of extreme subdwarfs covering 11.5<M_V_<14.5 in the M_V_ vs V-I diagram. The transformation to the M_bol_ vs log T_eff_ plane is presented and the results are compared with various model interior computations. Within the limitations due to the uncertain T_eff_ scale for cool dwarfs and subdwarfs, the coolest members of the extreme subdwarf sequence appear to be near the hydrogen-burning minimum mass limit for stars with metallicities of [M/H]~-2.
Trigonometric parallaxes, relative proper motions, and photometry are presented for 122 stars in 111 systems. Of these stars, 70 are brighter than V = 10.0.
Accurate positional measurements of planets and satellites are used to improve our knowledge of both their orbits and their dynamics and to infer the accuracy of the planet and satellite ephemerides. In the framework of the European FP7 ESPaCE program, we provide the positions of Saturn and its major satellites taken with the U.S. Naval Observatory 26-inch refractor from 1974 to 1998. 526 astrophotographic plates were measured with the digitizer of the Royal Observatory of Belgium and reduced through an optimal process that includes image, instrumental, and spherical corrections using the UCAC4 catalog to provide the most accurate equatorial (RA, DEC) positions.
This paper provides expressions to be used to implement the new definition of UT1 corresponding to the IAU 2000 resolutions either in the new (CEO-based) or classical (equinox-based) transformations between the International Terrestrial Reference System (ITRS) and the Geocentric Celestial Reference System (GCRS). The new expression for Greenwich Sidereal Time (GST) has to be in agreement at the micro-arcsecond level, for one century, with the IAU 2000 expressions for the Earth Rotation Angle (ERA) and for the quantity s positioning the Celestial Ephemeris Origin (CEO) on the equator of the CIP. The computations of the new expressions using the IAU 2000 precession-nutation model are performed in such a manner as to ensure that there is no discontinuity in UT1 on 1 January 2003 and that there is equivalence of the classical and new transformations between the ITRS and GCRS relative to the rotation about the axis of the CIP when these expressions are used. The equinox offset that is considered in the computations refers to the dynamical mean equinox of J2000.0. The resulting expressions have been included in the IERS Conventions 2000.
