ACDS V10.0 - Detailed Description of I/322A

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

| # Detailed Description of I/322A : UCAC4 Catalogue (Zacharias+, 2012) |

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/322A              UCAC4 Catalogue                 (Zacharias+, 2012)
    ================================================================================
    The fourth U.S. Naval Observatory CCD Astrograph Catalog (UCAC4)
         Zacharias N., Finch C.T., Girard T.M., Henden A., Bartlett J.L.,
         Monet D.G., Zacharias M.I.
        <Astron. J. 145, 44 (2013)>
        =2012yCat.1322....0Z
        =2013AJ....145...44Z
    ================================================================================
    ADC_Keywords: Surveys ; Positional data ; Proper motions

    Description:
        UCAC4 is a compiled, all-sky star catalog covering mainly the 8 to 16
        magnitude range in a single bandpass between V and R. Positional
        errors are about 15 to 20 mas for stars in the 10 to 14 mag range.
        Proper motions have been derived for most of the about 113 million
        stars utilizing about 140 other star catalogs with significant epoch
        difference to the UCAC CCD observations. These data are supplemented
        by 2MASS photometric data for about 110 million stars and 5-band
        (B,V,g,r,i) photometry from the APASS (AAVSO Photometric All-Sky
        Survey) for over 50 million stars. UCAC4 also contains error estimates
        and various flags. All bright stars not observed with the astrograph
        have been added to UCAC4 from a set of Hipparcos and Tycho-2 stars.
        Thus UCAC4 should be complete from the brightest stars to about R=16,
        with the source of data indicated in flags. UCAC4 also provides a link
        to the original Hipparcos star number with additional data such as
        parallax found on a separate data file included in this release.

        The proper motions of bright stars are based on about 140 catalogs,
        including Hipparcos and Tycho, as well as all catalogs used for the
        Tycho-2 proper motion construction. Proper motions of faint stars are
        based on re-reductions of early epoch SPM data (-90 to about -20 deg
        Dec) and NPM (PMM scans of early epoch blue plates) for the remainder
        of the sky. These early epoch SPM data have also been combined with
        late epoch SPM data to arrive at proper motions partly independent
        from UCAC4 (Girard et al. 2011AJ....142...15G, Cat. I/320). The NPM
        data used in UCAC4 are not published. No Schmidt plate data are used
        in UCAC4.

        The unpublished plate measure data obtained by StarScan from the AGK2,
        the Hamburg Zone Astrograph, the USNO Black Birch Astrograph, and the
        Lick Astrograph have contributed to considerable improvement in proper
        motions for stars mainly in the 10 to 14 mag range (down to the UCAC
        limit for Lick data); however, these data do not cover all sky.

        Recources permitting, USNO plans to release the individual CCD
        observations (RA,Dec at epoch of each CCD observations) in the future.
        Please contact nz@usno.navy.mil if you are interested in obtaining
        this set of about 50 GB data. We will likely request that interested
        users provide an external disk drive for the data release.

    Acknowledging UCAC4:
        The paper (Zacharias et al., 2013, AJ, 145, 44) should be cited
        whenever UCAC4 data is utilized.

    File Summary:

           FileName      Lrecl  Records   Explanations

    ×                   80        .   This file
    × ReadMe            80        .   This file
    × out.sam          300     1000   Sample UCAC4 output (out of 113780093 stars)
    × ucac4doc.txt      79     2008   Description of UCAC4 (readme_u4)

    See also:
      http://www.usno.navy.mil/USNO/astrometry/optical-IR-prod/ucac : UCAC home page
       I/289 : UCAC2 Catalogue (Zacharias+ 2004)
       I/315 : UCAC3 Catalogue (Zacharias+ 2009)
       I/247 : The AC2000 Catalogue (Urban+ 1997)
       I/259 : The Tycho-2 Catalogue (Hog+ 2000)
       I/264 : Sixth Catalogue of Fundamental Stars (FK6) (Wielen+ 2000)
       I/277 : SPM Catalog 2.0 (Platais+ 1998)
       I/317 : The PPMXL Catalog (Roeser+ 2010)
      II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
     VII/233 : The 2MASS Extended sources (IPAC/UMass, 2003-2006)
     VII/242 : LEDA galaxies with DENIS measurements catalog (Paturel+, 2005)
     VII/248 : Quasars and Active Galactic Nuclei (12th Ed.) (Veron+ 2006)

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

       Bytes Format Units   Label    Explanations

       1- 10  A10   ---     UCAC4    UCAC4 recommended identifier (ZZZ-NNNNNN) (1)
      12- 22  F11.7 deg     RAdeg    Mean right ascension , Ep=J2000 (2)
      24- 34  F11.7 deg     DEdeg    Mean declination , Ep=J2000 (2)
      36- 38  I3    mas     e_RAdeg  Mean error of RAdeg at mean epoch
      40- 42  I3    mas     e_DEdeg  Mean error of DEdeg at mean epoch
      44- 47  I4    mas     ePos     Total mean error on position at Ep=J2000 (3)
      49- 55  F7.2  yr      EpRA     Central epoch for mean RA
      57- 63  F7.2  yr      EpDE     Central epoch for mean Declination
      65- 70  F6.3  mag     f.mag    ? UCAC fit model magnitude (579-642nm) (4)
      72- 77  F6.3  mag     a.mag    ? UCAC aperture magnitude (579-642nm) (4)
      79- 82  F4.2  mag     e_a.mag  ? Mean error on f.mag and a.mag (5)
          84  I1    ---     of       [0/9] UCAC4 object classification flag (6)
      86- 87  I2    ---     db       [0/36] UCAC4 double star flag (7)
      89- 90  I2    ---     Na       [0/71] Number of UCAC observations for
                                         the star
      92- 93  I2    ---     Nu       [0/70] Number of used UCAC observations (8)
      95- 96  I2    ---     Nc       [1/38] Number of catalog positions used
                                         for pm
      98-104  F7.1  mas/yr  pmRA     ? Proper motion in RA(*cos(Dec)) (9)
     106-112  F7.1  mas/yr  pmDE     ? Proper motion in Dec (9)
     114-117  F4.1  mas/yr  e_pmRA   ? Mean error on pmRA (9)
     119-122  F4.1  mas/yr  e_pmDE   ? Mean error on pmDE (9)
     124-132  I9    ---     MPOS1    [1/182895114] Unique star ID number (10)
     134-143  A10   ---     UCAC2    UCAC2 (Cat. I/289) designation (ZZZ-NNNNNN)
     145-156  A12   ---     Tycho-2  Tycho-2 (Cat. I/259) designation
                                         (FFFF-NNNNN-N)
     158-167  I10   ---     2Mkey    ? 2MASS (Cat. II/246) Unique source
                                        identifier
     169-174  F6.3  mag     Jmag     ? 2MASS J magnitude (1.2um)
     176-179  F4.2  mag     e_Jmag   ? Mean error (rounded to 0.01mag)
     181-182  I02   ---     q_Jmag   [0,58]? J-band quality-confusion flag (11)
     184-189  F6.3  mag     Hmag     ? 2MASS H magnitude (1.6um)
     191-194  F4.2  mag     e_Hmag   ? Mean error (rounded to 0.01mag)
     196-197  I02   ---     q_Hmag   [0,58]? H-band quality-confusion flag (11)
     199-204  F6.3  mag     Kmag     ? 2MASS Ks magnitude (2.2um)
     206-209  F4.2  mag     e_Kmag   ? Mean error (rounded to 0.01mag)
     211-212  I02   ---     q_Kmag   [0,58]? K-band quality-confusion flag (11)
     214-219  F6.3  mag     Bmag     ? B magnitude from APASS (12)
         221  A1    ---     f_Bmag   [.-] Actual or S/N estimated error (12)
     223-224  I2    cmag    e_Bmag   ? Estimated error on Bmag (12)
     226-231  F6.3  mag     Vmag     ? V magnitude from APASS (12)
         233  A1    ---     f_Vmag   [.-] Actual or S/N estimated error (12)
     235-236  I2    cmag    e_Vmag   ? Estimated error on Vmag (12)
     238-243  F6.3  mag     gmag     ? g magnitude from APASS (12)
         245  A1    ---     f_gmag   [.-] Actual or S/N estimated error (12)
     247-248  I2    cmag    e_gmag   ? Estimated error on gmag (12)
     250-255  F6.3  mag     rmag     ? r magnitude from APASS (12)
         257  A1    ---     f_rmag   [.-] Actual or S/N estimated error (12)
     259-260  I2    cmag    e_rmag   ? Estimated error on rmag (12)
     262-267  F6.3  mag     imag     ? i magnitude from APASS (12)
         269  A1    ---     f_imag   [.-] Actual or S/N estimated error (12)
     271-272  I2    cmag    e_imag   ? Estimated error on imag (12)
         274  I1    ---     g        [0,3] g-flag from SPM (13)
         276  I1    ---     c        [0,7] c-flag from SPM (14)
         278  I1    ---     H        [0/9] Hipparcos/Tycho flag (15)
         280  I1    ---     A        [0/8] AC2000 flag (16)
         282  I1    ---     b        [0/8] AGK2 Bonn match flag (16)
         284  I1    ---     h        [0/8] AGK2 Hamburg match flag (16)
         286  I1    ---     Z        [0/8] Zone astrographic match flag (16)
         288  I1    ---     B        [0/8] Black Birch match flag (16)
         290  I1    ---     L        [0/8] Lick Astrographic match flag (16)
         292  I1    ---     N        [0/8] NPM Lick match flag (16)
         294  I1    ---     S        [0/8] SPM Lick match flag (16)
     296-297  I2  [6arcsec] LEDA     LEDA I-band galaxy match (17)
     299-300  I2    arcsec  2MX      2MASX K-band match (18)

    Note (1): the UCAC4 number is the recommended identification of UCAC4 stars.
         It made as "ZZZ-NNNNNNN", where zzz is the zone number (between 1 and
         900 from South pole to North pole, each zone being 0.2° wide), and
         nnnnnn the 6-digit running number in the zone.
    Note (2): Positions are on the International Celestial Reference System
         (ICRS) as represented by the Hipparcos / Tycho-2  catalogs. The epoch
         for the positions of all stars is J2000.0: the weighted mean catalog
         position was updated using the proper motions. The observational UCAC
         position is but one of several going into these values and is not
         given in the UCAC4; thus the original UCAC observation cannot be
         recovered from these data.
    Note (3): taking into account the propagation of the proper motion error
         between the mean epoch and J2000.
    Note (4): systematic errors are expected to be below 0.1mag. The aperture
         photometry (a.mag) is considered more robust, particularly for "odd"
         cases, while the model fit magnitude is expected to be more accurate
         for "well behaved" stars.
    Note (5): For many stars a photometric error based on the scatter from
         individual observations of that star on different CCD frames could be
         obtained.  A model error was also attempted to be assigned, based on
         the S/N ratio.  The error quoted here is the larger of the 2.  If that
         error exceeds 0.9mag the error was set to 0.9mag
    Note (6): the object type flag is used to identify possible problems
        with a star and has the following meaning:
        0 = good, clean star, no known problem
        1 = near overexposed star
        2 = possible streak object
        3 = high proper motion (HPM) star
        4 = actually use external HPM data instead of UCAC4 observed data
            (accuracy of positions varies between catalogs)
        5 = poor proper motion solution, report only CCD epoch position
        6 = substitute poor astrometric results by FK6/Hip/Tycho-2 data
        7 = added supplement star (no CCD data) from FK6/Hip/Tycho-2 data,
            and 2 stars added from high proper motion surveys
        8 = high proper motion solution in UCAC4, star not matched with PPMXL
        9 = high proper motion solution in UCAC4, discrepant motion to PPMXL
    Note (7): The double star flag is used to indicate the type/quality
         of double star fit. It is a combination of 2 flags, dsf+dst:
      * dsf = double star flag, represents the overall classification:
          0 = single star
         10 = component #1 of "good" double star
         20 = component #2 of "good" double star
         30 = blended image
      * dst = double star type, derived from pixel data image profile fits
              (largest value of all images used for this star):
          0 = no double star, not sufficient #pixels or elongation
              to even call double star fit subroutine
          1 = elongated image but no more than 1 peak detected
          2 = 2 separate peaks detected -> try double star fit
          3 = secondary peak found on each side of primary
          4 = case 1 after successful double fit (small separation, blended image)
          5 = case 2 after successful double fit (most likely real double)
          6 = case 3 after successful double fit (brighter secondary picked)
    Note (8): A zero for the number of used images indicates that all images
         have some "problem" (such as overexposure). In that case an unweighted
         mean over all available images (Na) is taken to derive the mean
         position, while normally a weighted mean was calculated based on the
         "good" images, excluding possible problem images (Nu<=Na).
    Note (9):  For astrometric data copied from the FK6, Hipparcos and Tycho-2
         catalogs a mean error in positions was adopted depending on input
         catalog and the brightness of the star rather than giving the
         individual star's error quoted in those catalogs.
    Note (10):  This unique star identification number is between 200001 and
         321640 for Hipparcos stars, and between 1 and 9430 for non-Hipparcos
         stars supplemented to the UCAC4 catalog (no CCD observation). For all
         other stars this unique star identification number is the internal
         mean-position-file (MPOS) number + 1million. Note, there are several
         thousand cases where different UCAC4 stars link to the same Hipparcos
         star number due to resolved binary stars with each component being a
         separate star entry in UCAC4.
    Note (11): For each 2MASS bandpass a combined flag was created
         (cc_flg + ph_qual) consisting of the contamination flag (0 to 50)
         and the photometric quality flag (0 to 8).
           0 =  cc_flg 2MASS '0', no artifacts or contamination
          10 =  cc_flg 2MASS 'p', source may be contaminated by a latent image
          20 =  cc_flg 2MASS 'c', photometric confusion
          30 =  cc_flg 2MASS 'd', diffraction spike confusion
          40 =  cc_flg 2MASS 's', electronic stripe
          50 =  cc_flg 2MASS 'b', bandmerge confusion
           0 = no ph_qual flag
           1 = ph_qual 2MASS 'X', no valid brightness estimate
           2 = ph_qual 2MASS 'U', upper limit on magnitude
           3 = ph_qual 2MASS 'F', no reliable estimate of the photometric error
           4 = ph_qual 2MASS 'E', goodness-of-fit quality of profile-fit poor
           5 = ph_qual 2MASS 'A', valid measurement, snr>10 AND cmsig<0.10857
           6 = ph_qual 2MASS 'B', valid measurement, snr> 7 AND cmsig<0.15510
           7 = ph_qual 2MASS 'C', valid measurement, snr> 5 AND cmsig<0.21714
           8 = ph_qual 2MASS 'D', valid measurement, no snr OR cmsig req.

         For example the value 05 is decoded to be cc_flg=0, and ph_qual=5,
         meaning no artifacts or contamination and 2MASS qual flag = "A".
    Note (12): Data are from the AAVSO Photometric all-sky survey (APASS) DR6
         plus single observation stars kindly provided by A.Henden. For bright
         stars the Bmag and Vmag columns contain the Hipparcos/Tycho Bt and Vt
         mags respectively, whenever there is no APASS B or V available and
         valid Bt or Vt mags were found. The errors flagged with "-" are formal
         errors estimated from the S/N, while the "normal" errors (flagged with
         ".") are from the official release data error estimates (at least 2
         observations per star).
    Note (13): The g-flag from the Yale San Juan first epoch Southern
         Proper Motion data (YSJ1, SPM) has the following meaning:
         0 = no info
         1 = matched with 2MASS extended source list (2MASX
         2 = LEDA  galaxy
         3 = known QSO
    Note (14): The c-flag from the Yale San Juan first epoch Southern Proper
         Motion data (YSJ1, SPM) indicates which input catalog has been used
         to identify stars for pipeline processing:
         1 = Hipparcos (Cat. I/311)
         2 = Tycho2 (Cat. I/259)
         3 = UCAC2 (Cat. I/289)
         4 = 2MASS psc (Cat. II/246)
         5 = 2MASS xsc (extended sources, Cat. VII/233; largely galaxies)
         6 = LEDA  (confirmed galaxies, Paturel et al. 2005)
         7 = QSO   (Veron-Cetty & Veron 2006, Cat. VII/248)
    Note (15): The FK6-Hipparcos-Tycho-source-flag has the following meaning:
         0 = not a Hipparcos or Tycho star
         1 = Hipparcos 1997 version main catalog (Cat I/239)
         2 = Hipparcos double star annex
         3 = Tycho-2 (Cat. I/259)
         4 = Tycho annex 1
         5 = Tycho annex 2
         6 = FK6 position and proper motion (instead of Hipparcos data)
         7 = Hippparcos 2007 solution position and proper motion (Cat. I/311)
         8 = FK6, only PM substitution (not in UCAC4 data)
         9 = Hipparcos 2007, only proper motion substituted (Cat. I/311)
    Note (16): The catflg match flag is provided for major catalogs used
         in the computation of the proper motions.  Each match is analyzed
         for multiple matches of entries of the 1st catalog to 2nd catalog
         entries, and the other way around.  Matches are also classified
         by separation and difference in magnitude to arrive at a confidence
         level group.  The flag has the following meaning:
         0 = star not matched with this catalog
         1 = unique-unique match, not involving a double star
         2 = unique-unique match, but involving a flagged double star
         3 = multiple match but unique in high confidence level group, no double
         4 = as 3, but involving a flagged double star
         5 = closest match, not involving a double, likely o.k.
         6 = closest match, but involving a flagged double star
         7 = maybe o.k. smallest separation match in both directions, no double
         8 = as 7, but involving a flagged double star
    Note (17): value is either 0 (no match) or contains the log of the apparent
         total diameter (in 0.1arcmin) for I-band (object size) information
         copied from the LEDA catalog (galaxies). A size value of less than 1
         has been rounded up to 1.
    Note (18): This flag is either 0 (no match) or contains the length of the
         semi-major axis of the fiducial ellipse at the K-band (object size)
         information copied from the 2MASS extended source catalog.

    Acknowledgements:
        It is a pleasure to thank Norbert Zacharias, who wrote most of
        this introduction and answered to many questions.

    History:

      * 01-Aug-2012: Original version

      * 30-Jan-2013 (version 'A'): Fix 3416 high proper motion stars
        The fix concerns 3416 stars in 416 binary zone files between
        6 and 449. All affected stars have object type flag = 4, i.e.
        stars observed with the astrograph and mean position and proper
        motion taken from external catalogs. Only the proper motion
        columns are affected by this bug, all other data items of those
        stars remain as they are in the UCAC4. The Python script file
        "modifs.py" patches the original zone files.
      * 23-Aug-2024:  format migration (CDS) with minor metadata updates
    ================================================================================
    (End)         Norbert Zacharias [USNO], Francois Ochsenbein [CDS]    24-Jul-2012