ACDS V10.0 - Wed Apr 17 12:43:58 CEST 2019
 |
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