Tycho-2 Catalogue

C2A can access and display the Tycho-2 catalogue. This catalogue gives the positions, proper motions, the BT and VT magnitudes for 2.5 million stars from the whole celestial sphere. The density of stars varies from 25 stars per square degree at the galactic poles to up to 150 stars per square degree in the galactic plane. The positions and magnitudes of the stars in the Tycho-2 catalogue have been derived from a new reduction of Tycho data obtained by the ESA Hipparcos satellite. The proper motions of almost all the stars in the Tycho-2 catalogue have been derived from an analysis of 144 astrometric catalogues (obtained by ground-based telescopes). You select the Tycho-2 catalogue as the current catalogue through the Stars tab of the Options dialogue box, or by SHIFT-right-clicking on the map.

C2A takes into account the proper motions given in the Tycho-2 catalogue in determining star positions at a date specified by the user.

If you have the original Tycho-2 catalogue, the Tools page of the C2A Website provides a tool for compiling it in the C2A format. All the information needed to compile the catalogue is given on that page. Note that the Tycho2 catalogue directly compiled for C2A is available on the C2A website (http://astrosurf.com/c2a/english). The latest version of the compiler takes into account the two supplements to the Tycho-2 catalogue.

The information reported for each star is in the standard form of the Tycho-2 catalogue. The description of the fields given in the Tycho-2 documentation is provided below.

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.

Further  information on the Tycho-2 catalogue can be found on the Tycho-2 home page at: http://www.astro.ku.dk/~erik/Tycho-2.

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