The Tycho-2 Catalogue: Format Description

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

• 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_s2	+= 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.