{
  "id": "I/259",
  "title_cds": "The Tycho-2 Catalogue",
  "title_create": "Hog+ 2000",
  "year": "2000",
  "author": "Hog E., Fabricius C., Makarov V.V., Urban S., Corbin T.,Wycoff G., Bastian U., Schwekendiek P., Wicenec A.",
  "title_pub": " The Tycho-2 Catalogue of the 2.5 Million Brightest Stars",
  "first_author": "Hog E.",
  "bibcode": [
    "2000A&A...355L..27H"
  ],
  "ref_biblio": [
    "<Astron. Astrophys. 355, L27 (2000)>"
  ],
  "keyword_cds": [
    "Positional data",
    "Proper motions",
    "Surveys",
    "Photometry",
    "Stars, double and multiple"
  ],
  "keyword_pub": "astrometry - stars: fundamental parameters - catalogs",
  "mission": "Hipparcos",
  "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)",
    "V_T_ < 9 mag                           7 mas",
    "all stars, positions                   60 mas",
    "all stars, proper motions              2.5 mas/yr",
    "Photometric std. errors (3) on V_T_",
    "V_T_ < 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 10^6^",
    "------------------------------------------------------------",
    "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 V_T_ > 9 mag is below 1.5",
    "------------------------------------------------------------"
  ],
  "curator": "C. Fabricius  [Niels Bohr Institute]",
  "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"
  ],
  "tables": [
    {
      "name": "tyc2.dat",
      "desc": "*The Tycho-2 main catalogue"
    },
    {
      "name": "suppl_1.dat",
      "desc": "The Tycho-2 supplement-1"
    },
    {
      "name": "suppl_2.dat",
      "desc": "The Tycho-2 supplement-2"
    },
    {
      "name": "index.dat",
      "desc": "Index to Tycho-2 and supplement-1"
    },
    {
      "name": "guide.ps",
      "desc": "Guide to Tycho-2 (postscript)"
    },
    {
      "name": "guide.pdf",
      "desc": "Guide to Tycho-2 (pdf)"
    }
  ],
  "archive_date_creation": "08-Feb-2000",
  "catid": 1259,
  "vizier_date_update": "07-Feb-2000",
  "xmatch": "I/259/suppl_1",
  "doi_pub": [
    ""
  ],
  "alias": "Tycho-2",
  "records": "2539913 stars",
  "archive_date_update": "25-Jul-2023",
  "uat": [
    "Astrometry",
    "Proper motions",
    "Surveys",
    "Photometry",
    "Multiple stars"
  ],
  "ip_addr": "216.73.216.109",
  "data_access": "v-f"
}