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

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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 55 100 *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 (ICRS) mean of blue/red plates 25- 34 F10.6 deg DEdeg Declination (ICRS) mean of blue/red plates 35 A1 --- ACTflag [A] 'A' when star belongs to ACT (Cat. I/246) 36 A1 --- Mflag [*] '*' magnitudes are probably wrong 38- 41 F4.1 mag Bmag Magnitude from blue plate 43- 46 F4.1 mag Rmag Magnitude from red plate 48- 55 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 ================================================================================ (End) Francois Ochsenbein [CDS] 27-Oct-1998