ACDS V10.0 - Detailed Description of I/252

ACDS V10.0 - Sun Jan 19 07:49:50 CET 2025

| # Detailed Description of I/252 : The USNO-A2.0 Catalogue (Monet+ 1998) |

Note : this is the description file of the original catalog. This HTML page corresponds well to the original description, but some minor changes in the format may have been introduced in the FITS output files in order to allow for arithmetic operations on quantities such as coordinates and times. h:m:s and d:m:s units are normally converted into degrees, and YYYY-MM-DD into julian days.
Similarly, some slight changes may have been introduced in the units; the value given in the HTML files supersedes the value indicated in the ReadMe file for this catalogue.

    I/252            The USNO-A2.0 Catalogue                     (Monet+ 1998)
    ================================================================================
    USNO-A V2.0, A Catalog of Astrometric Standards
         Monet D.
         Bird A., Canzian B., Dahn C., Guetter H., Harris H., Henden A.,
         Levine S., Luginbuhl C., Monet A.K.B., Rhodes A., Riepe B.,
         Sell S., Stone R., Vrba F., Walker R.
        <U.S. Naval Observatory Flagstaff Station (USNOFS) and
         Universities Space Research Association (USRA) stationed at USNOFS.
         (1998)>
    ================================================================================
    ADC_Keywords: Surveys ; Positional data

    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.

    File Summary:

           FileName      Lrecl  Records   Explanations

    ×                   80        .   This file
    × ReadMe            80        .   This file
    × out.sam           58     1000  *Sample output (out of 526,280,881 stars)
    × read.me           79      353   Author's Original Catalogue Description
    × usnoa/*            0        .   Compact version of Catalogue (3.6Gbytes)

    Note on out.sam: this file is actually the result of the execution
         of the query on the compacted version of USNO-A2.0 at CDS
         (in subdirectory usnoa, not yet accessible)

    See also:
        ftp://ftp.nofs.navy.mil/usnoa : The Flagstaff FTP site with
             the original catalogue
        http://www.usno.navy.mil/pmm/ : The Precision Measuring Machine
             home page at Flagstaff Station, U.S. Naval Observatory

    Byte-by-byte Description of file:  out.sam

       Bytes Format Units   Label     Explanations

       1- 13  A13   ---    USNO-A2.0 *Original designation in USNO-A2.0 catalogue
      15- 24  F10.6 deg     RAdeg     Right ascension (FK5) mean of blue/red plates,
                                     Equinox J2000
      26- 35  F10.6 deg     DEdeg     Declination (FK5) mean of blue/red plates,
                                     Equinox J2000
          37  A1    ---     ACTflag   [A] 'A' when star belongs to ACT (Cat. I/246)
          39  A1    ---     Mflag     [*] '*' magnitudes are probably wrong
      41- 44  F4.1  mag     Bmag      Magnitude from blue plate
      46- 49  F4.1  mag     Rmag      Magnitude from red plate
      51- 58  F8.3  yr      Epoch    *?=0.0 Mean epoch of position

    Note on USNO-A2.0:
        This number allows to retrieve the exact original record: it is made
        of a zone number (4 digits from 0000 to 1725 representing the distance
        in 0.1deg to the South Pole, stepped by 75 = 7.5degrees), a dash (-)
        and a number in the area (8 digits, order by IRCS (J2000) RA);
        ****Note that this number differs from the USNO-A1.0 one.
    Note on Epoch:
        Epoch is the averaged date of observation between the blue and
        the red plates.

    Author's Address:
       Dave Monet
       US Naval Observatory Flagstaff Station
       PO Box 1149  (US Mail Only)
       West Highway 66  (FedEx, UPS, etc.)
       Flagstaff AZ 86001 USA

       Voice: 520-779-5132
       FAX:   520-774-3626
       e-mail:  dgm@nofs.navy.mil

    History:
       * 26-Aug-2024: format migration (CDS) with minor metadata updates
    ================================================================================
    (End)                                     Francois Ochsenbein [CDS]  27-Oct-1998