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Content of the Tycho-2 CD-ROM readme.txt : file with a short description of the Tycho-2 Catalogue format.txt : file with formats of the four catalogue files, also described in the Guide. data/ : directory with the catalogue files. The main catalogue (catalog.dat, 528 301 904 bytes), the two much shorter supplements (suppl_1.dat and suppl_2.dat), and the index file (index.dat). docs/ : directory with documentation. Guide to the Tycho-2 Catalogue (guide.pdf and .ps), the two figures from the Guide as high quality postscript files, and two papers submitted to Astron. Astrophys. about the catalogue (aa2000a.pdf and .ps) and about its construction and verification (aa2000b.pdf and .ps). You may want to consult the Tycho-2 home page: http://www.astro.ku.dk/~erik/Tycho-2 for updates and for further information. A perl program for extracting data from the catalogue is available from: http://archive.eso.org/ASTROM/ The Tycho-2 Catalogue 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 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. Components of double stars with separations down to 0.8 arcsec are included. The Tycho-2 positions and magnitudes are based on precisely the same observations as the Tycho-1 Catalogue (ESA SP-1200, 1997) 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. Proper motions precise to about 2.5 mas/yr are given as derived from a comparison with the Astrographic Catalogue (AC) and 143 other ground-based astrometric catalogues, all reduced to the Hipparcos celestial coordinate system. For only about 100,000 stars, no proper motion could be derived. Tycho-2 supersedes Tycho-1, and the ACT and TRC catalogues based on Tycho-1. The main catalogue, catalog.dat, gives: 1. For ALL entries: The observational Tycho-2 results (i.e. position and one or two magnitudes), at the epoch of observation. 2. For most entries (96%): Proper motions (at epoch 2000) derived using other catalogues (mainly AC) and the corresponding mean positions at epoch J2000, as well as mean epochs and error estimates. For double stars resolved in Tycho-2, but where the proper motion is for the photocentre, the same mean values are given to both components. When no proper motion has been derived, no mean position for epoch J2000 is given. Supplement-1, suppl_1.dat, gives: This file contains stars missing in Tycho-2, but found in HIP or Tycho-1. The supplement-1 only includes Tycho-1 stars of good quality and therefore the quality 9 (very poor) stars and probable side-lobes were not included. Supplement-2, suppl_2.dat, gives: This file contains the probable Tycho-1 sidelobes (quality 1-8) which were excluded from supplement-1. These stars are either false entries in Tycho-1 or stars where the result is heavily disturbed by nearby, much brighter stars. The quality 9 stars were also excluded from supplement-2. A look-up table, index.dat, is provided for the main catalogue and supplement-1. This file can be used to quickly find all stars located in a given field. This file gives descriptions of the formats of the data files. They are also given in the file "guide.ps" (or guide.pdf) in the docs directory. File Summary: -------------------------------------------------------------------------------- File Name Lrecl Records Explanations -------------------------------------------------------------------------------- catalog.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 -------------------------------------------------------------------------------- Records are terminated with \r\n (CR,LF), making the physical record lengths two characters longer. 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. In the format descriptions, the vertical bars are indicated as "1X". If a numerical field may be blank, this is indicated by a question mark following the range specification in the Explanations column, e.g. "[]?". Byte-by-byte description of file: catalog.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 4 I4.4 --- TYC1 [1,9537]+= TYC1 from TYC or GSC (1) 6- 10 I5.5 --- TYC2 [1,12121] TYC2 from TYC or GSC (1) 12- 13 I1,1X --- TYC3 [1,3] TYC3 from TYC (1) 14- 15 A1,1X --- pflag [ PX] mean position flag (2) 16- 28 F12.8,1X deg mRAdeg []? Mean Right Asc, ICRS, epoch J2000 (3) 29- 41 F12.8,1X deg mDEdeg []? Mean Decl, ICRS, at epoch J2000 (3) 42- 49 F7.1,1X mas/yr pmRA* [-4418.0,6544.2]? prop. mot. in RA*cos(dec) 50- 57 F7.1,1X mas/yr pmDE [-5774.3,10277.3]? prop. mot. in Dec 58- 61 I3,1X mas e_mRA* [3,183]? s.e. RA*cos(dec),at mean epoch (5) 62- 65 I3,1X mas e_mDE [1,184]? s.e. of Dec at mean epoch (5) 66- 70 F4.1,1X mas/yr e_pmRA* [0.2,11.5]? s.e. prop mot in RA*cos(dec)(5) 71- 75 F4.1,1X mas/yr e_pmDE [0.2,10.3]? s.e. of proper motion in Dec(5) 76- 83 F7.2,1X yr mepRA [1915.95,1992.53]? mean epoch of RA (4) 84- 91 F7.2,1X yr mepDE [1911.94,1992.01]? mean epoch of Dec (4) 92- 94 I2,1X --- Num [2,36]? Number of positions used 95- 98 F3.1,1X --- g_mRA [0.0,9.9]? Goodness of fit for mean RA (6) 99-102 F3.1,1X --- g_mDE [0.0,9.9]? Goodness of fit for mean Dec (6) 103-106 F3.1,1X --- g_pmRA [0.0,9.9]? Goodness of fit for pmRA (6) 107-110 F3.1,1X --- g_pmDE [0.0,9.9]? Goodness of fit for pmDE (6) 111-117 F6.3,1X mag BT [2.183,16.581]? Tycho-2 BT magnitude (7) 118-123 F5.3,1X mag e_BT [0.014,1.977]? s.e. of BT (7) 124-130 F6.3,1X mag VT [1.905,15.193]? Tycho-2 VT magnitude (7) 131-136 F5.3,1X mag e_VT [0.009,1.468]? s.e. of VT (7) 137-140 I3,1X --- prox [3,999] proximity indicator (8) 141-142 A1,1X --- TYC [ T] Tycho-1 star (9) 143-148 I6 --- HIP [1,120404]? Hipparcos number 149-152 A3,1X --- CCDM CCDM component identifier for HIP stars(10) 153-165 F12.8,1X deg RAdeg Observed Tycho-2 Right Ascension, ICRS 166-178 F12.8,1X deg DEdeg Observed Tycho-2 Declination, ICRS 179-183 F4.2,1X yr epRA [0.81,2.13] epoch-1990 of RAdeg 184-188 F4.2,1X yr epDE [0.72,2.36] epoch-1990 of DEdeg 189-194 F5.1,1X mas e_RA* s.e.RA*cos(dec), of observed Tycho-2 RA (5) 195-200 F5.1,1X mas e_DE s.e. of observed Tycho-2 Dec (5) 201-202 A1,1X --- posflg [ DP] type of Tycho-2 solution (11) 203-206 F4.1 --- corr 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 photo- centre 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) 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 BT or VT 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. Byte-by-byte description of the files: suppl_1.dat and suppl_2.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 4 I4.4 --- TYC1 [2,9529]+= TYC1 from TYC (1) 6- 10 I5.5 --- TYC2 [1,12112] TYC2 from TYC (1) 12- 13 I1,1X --- TYC3 [1,4] TYC3 from TYC (1) 14- 15 A1,1X --- flag [HT] data from Hipparcos or Tycho-1 (2) 16- 28 F12.8,1X deg RAdeg Right Asc, ICRS, at epoch J1991.25 29- 41 F12.8,1X deg DEdeg Decl, ICRS, at epoch J1991.25 42- 49 F7.1,1X mas/yr pmRA* []? prop. mot. in RA*cos(dec) 50- 57 F7.1,1X mas/yr pmDE []? prop. mot. in Dec 58- 63 F5.1,1X mas e_RA* s.e. RA*cos(dec) 64- 69 F5.1,1X mas e_DE s.e. of Dec 70- 75 F5.1,1X mas/yr e_pmRA* []? s.e. prop mot in RA * cos(dec) 76- 81 F5.1,1X mas/yr e_pmDE []? s.e. of proper motion in Dec 82- 83 A1,1X --- mflag [ BVH] (3) 84- 90 F6.3,1X mag BT []? Tycho-1 BT magnitude (4) 91- 96 F5.3,1X mag e_BT []? s.e. of BT (4) 97-103 F6.3,1X mag VT []? Tycho-1 VT or Hp magnitude (4) 104-109 F5.3,1X mag e_VT []? s.e. of VT (4) 110-113 I3,1X --- prox [1,999] proximity indicator (5) 114-115 A1,1X --- TYC [ T] Tycho-1 star 116-121 I6 --- HIP [1,120404]? Hipparcos number 122-122 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. 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- 8 I7,1X --- rec_t2 + Tycho-2 rec. of 1st star in region (1) 9-15 I6,1X --- rec_s1 += Suppl-1 rec. of 1st star in region (1) 16-22 F6.2,1X deg RAmin [-0.01,] smallest RA in region (2) 23-29 F6.2,1X deg RAmax [,360.00] largest RA in region (2) 30-36 F6.2,1X 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.