ACDS V10.0 - Detailed Description of I/259

ACDS V10.0 - Mon Feb 03 17:08:19 CET 2025

| # Detailed Description of I/259 : The Tycho-2 Catalogue (Hog+ 2000) |

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/259           The Tycho-2 Catalogue              (Hog+ 2000)
    ================================================================================
    The Tycho-2 Catalogue of the 2.5 Million Brightest Stars
        Hog E., Fabricius C., Makarov V.V., Urban S., Corbin T.,
        Wycoff G., Bastian U., Schwekendiek P., Wicenec A.
       <Astron. Astrophys. 355, L27 (2000)>
       =2000A&A...355L..27H
    ================================================================================
    ADC_Keywords: Positional data ; Proper motions ; Surveys ;
                  Photometry ; Stars, double and multiple
    Mission_Name: Hipparcos

    Keywords: astrometry - stars: fundamental parameters - catalogs

    Abstract:
        The Tycho-2 Catalogue is an astrometric reference catalogue containing
        positions  and proper motions  as well as  two-colour photometric data
        for the 2.5 million brightest stars in the sky.  The Tycho-2 positions
        and magnitudes are  based on  precisely the  same observations  as the
        original  Tycho  Catalogue  (hereafter  Tycho-1;  see  Cat.  I/239))
        collected  by the  star mapper  of the  ESA Hipparcos  satellite,  but
        Tycho-2 is much bigger  and slightly  more precise,   owing to  a more
        advanced   reduction  technique.   Components  of  double  stars  with
        separations down to 0.8 arcsec are included. Proper motions precise to
        about 2.5 mas/yr are given as  derived  from  a  comparison  with  the
        Astrographic   Catalogue  and   143  other   ground-based  astrometric
        catalogues,  all reduced to the Hipparcos celestial coordinate system.
        Tycho-2  supersedes in most applications Tycho-1,   as well as the ACT
        (Cat.  I/246)  and TRC  (Cat. I/250)  catalogues based on Tycho-1.
        Supplement-1  lists stars  from the  Hipparcos and  Tycho-1 Catalogues
        which are not in Tycho-2.  Supplement-2 lists 1146 Tycho-1 stars which
        are probably either false or heavily disturbed.

        For more information, please consult the Tycho-2 home page:
        http://www.astro.ku.dk/~erik/Tycho-2

    Catalogue Characteristics:

        The principal characteristics of the Tycho-2 Catalogue are
        summarized below. By means of proper motions the positions
        are transferred to the year 2000.0, the epoch of the catalogue.
        The median values of internal standard errors are given.
        ------------------------------------------------------------
        Mean satellite observation epoch      ~J1991.5
        Epoch of the Tycho-2 Catalogue         J2000.0
        Reference system                       ICRS
          coincidence with ICRS (1)             ±0.6 mas
          deviation from inertial (1)           ±0.25 mas/yr
        Number of entries                      2,539,913
        Astrometric standard errors (2)
          VT < 9 mag                           7 mas
          all stars, positions                   60 mas
          all stars, proper motions              2.5 mas/yr
        Photometric std. errors (3) on VT
          VT < 9 mag                           0.013 mag
          all stars                              0.10 mag
        Star density
          b= 0 deg                             150 stars/sq.deg.
          b= ±30 deg                          50 stars/sq.deg.
          b= ±90 deg                          25 stars/sq.deg.
        Completeness to 90 per cent            V ~ 11.5 mag
        Completeness to 99 per cent            V ~ 11.0 mag
        Number of Tycho observations           ~300 106
        ------------------------------------------------------------
        Note (1): about all 3 axes
        Note (2):
            ratio of external to internal standard errors is ~1.0
            for positions and for proper motions. Systematic errors
            are less than 1 mas and 0.5 mas/yr
        Note (3):
            ratio of photometric external to internal standard errors
            at VT > 9 mag is below 1.5
        ------------------------------------------------------------

    File Summary:

           FileName      Lrecl  Records   Explanations

    ×                   80        .   This file
    × ReadMe            80        .   This file
    × tyc2.dat         206  2539913  *The Tycho-2 main catalogue
    × suppl_1.dat      122    17588   The Tycho-2 supplement-1
    × suppl_2.dat      122     1146   The Tycho-2 supplement-2
    × index.dat         42     9538   Index to Tycho-2 and supplement-1
    × guide.ps         120     7837   Guide to Tycho-2 (postscript)
    × guide.pdf          1   428724   Guide to Tycho-2 (pdf)

    Note on tyc2.dat:
        This huge file is split into 20 smaller files named tyc2.dat.00,
        tyc2.dat.01, ... tyc2.dat.18, each containing 127000 lines,
        and tyc2.dat.19 which contains the last 126913 lines.

    See also:
        I/239 : The Hipparcos and Tycho Catalogues (ESA 1997)
        I/211 : CCDM (Components of Double and Multiple stars) (Dommanget+ 1994)
        I/246 : The ACT Reference Catalog (Urban+ 1997)
        I/250 : The Tycho Reference Catalogue (Hog+ 1998)
        http://www.astro.ku.dk/~erik/Tycho-2 : Tycho-2 home page

    Nomenclature Notes:
        The TYC identifier is constructed from the GSC region number (TYC1),
        the running number within the region (TYC2) and a component identifier
        (TYC3) which is normally 1. Some non-GSC running numbers were
        constructed for the first Tycho Catalogue and for Tycho-2.
        The recommended star designation contains a hyphen between the TYC
        numbers, e.g. TYC 1-13-1.

    Field separator in the data files:
        In the data files, the fields in each record are separated by
        a vertical bar, |. In this connection the TYC identifier (TYC1, TYC2
        and TYC3) constitutes one field and the pair of a HIP number with a
        CCDM identifier is also considered one field.

    Byte-by-byte Description of file:  tyc2.dat

       Bytes Format   Units   Label    Explanations

       1-  4  I4      ---     TYC1     [1,9537]+= TYC1 from TYC or GSC (1)
       6- 10  I5      ---     TYC2     [1,12121]  TYC2 from TYC or GSC (1)
          12  I1      ---     TYC3     [1,3]      TYC3 from TYC (1)
          14  A1      ---     pflag    [ PX] mean position flag (2)
      16- 27  F12.8   deg     RAmdeg   []? Mean Right Asc, ICRS, epoch=J2000 (3)
      29- 40  F12.8   deg     DEmdeg   []? Mean Decl, ICRS, at epoch=J2000 (3)
      42- 48  F7.1    mas/yr  pmRA     ? Proper motion in RA*cos(dec) (12)
      50- 56  F7.1    mas/yr  pmDE     ? Proper motion in Dec (12)
      58- 60  I3      mas    e_RAmdeg  [3,183]? s.e. RA*cos(dec),at mean epoch (5)
      62- 64  I3      mas    e_DEmdeg  [1,184]? s.e. of Dec at mean epoch (5)
      66- 69  F4.1    mas/yr  e_pmRA   [0.2,11.5]? s.e. prop mot in RA*cos(dec)(5)
      71- 74  F4.1    mas/yr  e_pmDE   [0.2,10.3]? s.e. of proper motion in Dec(5)
      76- 82  F7.2    yr      EpRAm    [1915.95,1992.53]? mean epoch of RA (4)
      84- 90  F7.2    yr      EpDEm    [1911.94,1992.01]? mean epoch of Dec (4)
      92- 93  I2      ---     Num      [2,36]? Number of positions used
      95- 97  F3.1    ---    q_RAmdeg  [0.0,9.9]? Goodness of fit for mean RA (6)
      99-101  F3.1    ---    q_DEmdeg  [0.0,9.9]? Goodness of fit for mean Dec (6)
     103-105  F3.1    ---     q_pmRA   [0.0,9.9]? Goodness of fit for pmRA (6)
     107-109  F3.1    ---     q_pmDE   [0.0,9.9]? Goodness of fit for pmDE (6)
     111-116  F6.3    mag     BTmag    [2.183,16.581]? Tycho-2 BT magnitude (7)
     118-122  F5.3    mag     e_BTmag  [0.014,1.977]? s.e. of BT (7)
     124-129  F6.3    mag     VTmag    [1.905,15.193]? Tycho-2 VT magnitude (7)
     131-135  F5.3    mag     e_VTmag  [0.009,1.468]? s.e. of VT (7)
     137-139  I3    0.1arcsec prox     [3,999] proximity indicator (8)
         141  A1      ---     TYC      [T] Tycho-1 star (9)
     143-148  I6      ---     HIP      [1,120404]? Hipparcos number
     149-151  A3      ---     CCDM     CCDM component identifier for HIP stars(10)
     153-164  F12.8   deg     RAdeg    Observed Tycho-2 Right Ascension, ICRS
     166-177  F12.8   deg     DEdeg    Observed Tycho-2 Declination, ICRS
     179-182  F4.2    yr    EpRA-1990  [0.81,2.13]  epoch-1990 of RAdeg
     184-187  F4.2    yr    EpDE-1990  [0.72,2.36]  epoch-1990 of DEdeg
     189-193  F5.1    mas     e_RAdeg  s.e.RA*cos(dec), of observed Tycho-2 RA (5)
     195-199  F5.1    mas     e_DEdeg  s.e. of observed Tycho-2 Dec (5)
         201  A1      ---     posflg   [ DP] type of Tycho-2 solution (11)
     203-206  F4.1    ---     corr     [-1,1] correlation (RAdeg,DEdeg)

    Note (1): The TYC identifier is constructed from the GSC region number
        (TYC1), the running number within the region (TYC2) and a component
        identifier (TYC3) which is normally 1. Some non-GSC running numbers
        were constructed for the first Tycho Catalogue and for Tycho-2.
        The recommended star designation contains a hyphen between the
        TYC numbers, e.g. TYC 1-13-1.
    Note (2):
        ' ' = normal mean position and proper motion.
        'P' = the mean position, proper motion, etc., refer to the
              photocentre of two Tycho-2 entries, where the BT magnitudes
              were used in weighting the positions.
        'X' = no mean position, no proper motion.
    Note (3):
        The mean position is a weighted mean for the catalogues contributing
        to the proper motion determination. This mean has then been brought to
        epoch 2000.0 by the computed proper motion. See Note(2) above for
        details. Tycho-2 is one of the several catalogues used to determine
        the mean position and proper motion. The observed Tycho-2 position is
        given in the fields RAdeg and DEdeg.
    Note (4):
        The mean epochs are given in Julian years.
    Note (5):
        The errors are based on error models.
    Note (6):
        This goodness of fit is the ratio of the scatter-based and the
        model-based error. It is only defined when Num > 2. Values
        exceeding 9.9 are truncated to 9.9.
    Note (7):
        Blank when no magnitude is available. Either BTmag or VTmag is
        always given. Approximate Johnson photometry may be obtained as:
        V   = VT -0.090*(BT-VT)
        B-V = 0.850*(BT-VT)
        Consult Sect 1.3 of Vol 1 of "The Hipparcos and Tycho Catalogues",
        ESA SP-1200, 1997, for details.
    Note (8):
        Distance in units of 100 mas to the nearest entry in the Tycho-2
        main catalogue or supplement. The distance is computed for the
        epoch 1991.25. A value of 999 (i.e. 99.9 arcsec) is given if the
        distance exceeds 99.9 arcsec.
    Note (9):
        ' ' = no Tycho-1 star was found within 0.8 arcsec (quality 1-8)
              or 2.4 arcsec (quality 9).
        'T' = this is a Tycho-1 star. The Tycho-1 identifier is given in the
              beginning of the record. For Tycho-1 stars, resolved in
              Tycho-2 as a close pair, both components are flagged as
              a Tycho-1 star and the Tycho-1 TYC3 is assigned to the
              brightest (VT) component.
        The HIP-only stars given in Tycho-1 are not flagged as Tycho-1 stars.
    Note (10):
        The CCDM component identifiers for double or multiple Hipparcos stars
        contributing to this Tycho-2 entry. For photocentre solutions, all
        components within 0.8 arcsec contribute. For double star solutions any
        unresolved component within 0.8 arcsec contributes. For single star
        solutions, the predicted signal from close stars were normally
        subtracted in the analysis of the photon counts and such stars
        therefore do not contribute to the solution. The components are given
        in lexical order.
    Note (11):
        ' ' = normal treatment, close stars were subtracted when possible.
        'D' = double star treatment. Two stars were found. The companion is
              normally included as a separate Tycho-2 entry, but may have
              been rejected.
        'P' = photocentre treatment, close stars were not subtracted. This
              special treatment was applied to known or suspected doubles
              which were not successfully (or reliably) resolved in the
              Tycho-2 double star processing.
    Note (12): Some Hipparcos stars (having a positive number in the HIP column)
         have no proper motions; these are virtually all in multiple systems.

    Byte-by-byte Description of file:  suppl_1.dat,  suppl_2.dat

       Bytes Format   Units   Label    Explanations

       1-  4  I4      ---     TYC1     [2,9529]+= TYC1 from TYC (1)
       6- 10  I5      ---     TYC2     [1,12112]  TYC2 from TYC (1)
          12  I1      ---     TYC3     [1,4]      TYC3 from TYC (1)
          14  A1      ---     flag     [HT] data from Hipparcos or Tycho-1 (2)
      16- 27  F12.8   deg     RAdeg    Right Asc, ICRS, at epoch=J1991.25
      29- 40  F12.8   deg     DEdeg    Decl, ICRS, at epoch=J1991.25
      42- 48  F7.1    mas/yr  pmRA     []? Proper motion in RA*cos(dec)
      50- 56  F7.1    mas/yr  pmDE     []? Proper motion in Dec
      58- 62  F5.1    mas     e_RAdeg  s.e. RA*cos(dec)
      64- 68  F5.1    mas     e_DEdeg  s.e. of Dec
      70- 74  F5.1    mas/yr  e_pmRA   []? s.e. prop mot in RA * cos(dec)
      76- 80  F5.1    mas/yr  e_pmDE   []? s.e. of proper motion in Dec
          82  A1      ---     mflag    [ BVH] Note about Tycho magnitudes (3)
      84- 89  F6.3    mag     BTmag    []? Tycho-1 BT magnitude (4)
      91- 95  F5.3    mag     e_BTmag  []? s.e. of BT (4)
      97-102  F6.3    mag     VTmag    []?  Tycho-1 VT or Hp magnitude (4)
     104-108  F5.3    mag     e_VTmag  []? s.e. of VT (4)
     110-112  I3    0.1arcsec prox     [1,999] proximity indicator (5)
         114  A1      ---     TYC      [ T] Tycho-1 star
     116-121  I6      ---     HIP      [1,120404]? Hipparcos number
         122  A1      ---     CCDM     CCDM component identifier for HIP stars

    Note (1): The TYC identifier is constructed from the GSC region number (TYC1),
        the running number within the region (TYC2) and a component identifier
        (TYC3) which is normally 1. The numbers are copied from Tycho-1.
        (see the "Nomenclature Notes" section above)
    Note (2):
        'H' = data are from Hipparcos and include proper motion.
        'T' = data are from Tycho-1. No proper motion is given.
    Note (3):
        ' ' = both BT and VT given.
        'B' = only BT given.
        'V' = only VT given.
        'H' = Hp is given instead of VT. BT is blank.
    Note (4):
        Blank when no magnitude is available.
        For Hipparcos stars with no VT, Hp is given instead of VT, and BT is blank.
    Note (5):
        Distance in units of 100 mas to nearest Tycho-2 main or supplement
        entry. (Computed for the epoch 1991.25). A value of 999 (i.e. 99.9
        arcsec) is given if the distance exceeds 99.9 arcsec.

    Byte-by-byte Description of file:  index.dat

       Bytes Format  Units   Label     Explanations

       1-  7  I7     ---     rec_t2    +  Tycho-2 rec. of 1st star in region (1)
       9- 14  I6     ---     rec_s1    += Suppl-1 rec. of 1st star in region (1)
      16- 21  F6.2   deg     RAmin     [-0.01,] smallest RA in region (2)
      23- 28  F6.2   deg     RAmax     [,360.00] largest RA in region (2)
      30- 35  F6.2   deg     DEmin     smallest Dec in this region (2)
      37- 42  F6.2   deg     DEmax     largest Dec in this region (2)

    Note (1): The catalogue is sorted according to the GSC region numbers.
        The line i of the index file gives the record number in Tycho-2 of
        the first star in GSC region i. Line i+1 gives the record number +1
        of the last star in GSC region i. For Supplement-1, some regions are
        empty and line i and line i+1 give the same record number.
    Note (2): a safe rounding was applied. Minimum values are always
        rounded down and maximum values up.

    References:
      Hog E., Fabricius C., Makarov V.V., Bastian U., Schwekendiek P., Wicenec A.,
        Urban S., Corbin T., Wycoff G., "Construction and verification of the
        Tycho-2 Catalogue." =2000A&A...357..367H
    ================================================================================
    (End)                       C. Fabricius  [Niels Bohr Institute]     19-Jan-2000