14.4.8 tycho2

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

Columns description:

id : Tycho 2 identifier. The TYC identifier is constructed from the GSC region number (string)

Tycho 2 identifier. 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.

hip : [1,120404] Hipparcos number (int)

[1,120404]? Hipparcos number

tyc1 : [1,9537]+= TYC1 from TYC or GSC (string)

[1,9537]+= TYC1 from TYC or GSC

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.

tyc2 : [1,12121] TYC2 from TYC or GSC (string)

[1,12121] TYC2 from TYC or GSC

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.

tyc3 : [1,3] TYC3 from TYC (string)

[1,3] TYC3 from TYC

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.

id_tycho : Numeric tycho2 identifier (long)

These are the IDs as published in tycho2. In TYCHO-2 objects were identified by 3 numbers (TYC1,TYC2 and TYC3) and we have combined these into one complete number given by (TYC1*1000000.0d0)+(TYC2*10.0d0)+(TYC3*1.0d0)

tyc : [T] Tycho-1 star (string)

[T] Tycho-1 star

’ ’ = 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.

ra : Observed Tycho-2 Right Ascension, ICRS (double, Angle[deg])

Observed Tycho-2 Right Ascension, ICRS

dec : Observed Tycho-2 Declination, ICRS (double, Angle[deg])

Observed Tycho-2 Declination, ICRS

ra_deg : Observed Tycho-2 Right Ascension, ICRS (double, Angle[deg])

Observed Tycho-2 Right Ascension, ICRS

de_deg : Observed Tycho-2 Declination, ICRS (double, Angle[deg])

Observed Tycho-2 Declination, ICRS

ra_mdeg : Mean Right Asc, ICRS, epoch=J2000 (double, Angle[deg])

Mean Right Asc, ICRS, epoch=J2000

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.

de_mdeg : Mean Decl, ICRS, at epoch=J2000 (double, Angle[deg])

Mean Decl, ICRS, at epoch=J2000

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.

pm_ra : Proper motion in RA*cos(dec) (float, Angular Velocity[mas/year])

Proper motion in RA*cos(dec)

Some Hipparcos stars (having a positive number in the HIP column) have no proper motions; these are virtually all in multiple systems.

pm_de : Proper motion in Dec (float, Angular Velocity[mas/year])

Proper motion in Dec

Some Hipparcos stars (having a positive number in the HIP column) have no proper motions; these are virtually all in multiple systems.

ep_ra1990 : [0.81,2.13] epoch-1990 of RAdeg (float, Time[year])

ep_de1990 : [0.72,2.36] epoch-1990 of DEdeg (float, Time[year])

Epoch-1990 of de_deg

ep_ra_m : [1915.95,1992.53] mean epoch of RA. The mean epochs are given in Julian years. (float, Time[year])

Mean epoch of RA. The mean epochs are given in Julian years.

ep_de_m : [1911.94,1992.01] mean epoch of Dec. The mean epochs are given in Julian years. (float, Time[year])

Mean epoch of Dec. The mean epochs are given in Julian years.

num : [2,36] Number of positions used (short)

Number of positions used

e_ra_deg : s.e.RA*cos(dec), of observed Tycho-2 RA. The errors are based on error models. (double, Angle[mas])

s.e.RA*cos(dec), of observed Tycho-2 RA. The errors are based on error models.

e_de_deg : s.e. of observed Tycho-2 Dec. The errors are based on error models. (double, Angle[mas])

s.e. of observed Tycho-2 Dec. The errors are based on error models.

corr : [-1,1] correlation (RAdeg,DEdeg) (double)

Correlation (ra_deg, de_deg)

e_ra_mdeg : [3,183] s.e. RA*cos(dec),at mean epoch. The errors are based on error models. (double, Angle[mas])

s.e. RA*cos(dec),at mean epoch. The errors are based on error models.

e_de_mdeg : [1,184] s.e. of Dec at mean epoch. The errors are based on error models. (double, Angle[mas])

s.e. of Dec at mean epoch. The errors are based on error models.

e_pm_ra : [0.2,11.5] s.e. prop mot in RA*cos(dec).The errors are based on error models. (float, Angular Velocity[mas/year])

s.e. prop mot in RA*cos(dec). The errors are based on error models.

e_pm_de : [0.2,10.3] s.e. of proper motion in Dec. The errors are based on error models. (float, Angular Velocity[mas/year])

s.e. of proper motion in Dec. The errors are based on error models.

q_ra_mdeg : [0.0,9.9] Goodness of fit for mean RA (float)

Goodness of fit for mean RA

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.

q_de_mdeg : [0.0,9.9] Goodness of fit for mean Dec (float)

Goodness of fit for mean Dec

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.

q_pm_de : [0.0,9.9] Goodness of fit for pmDE (float)

Goodness of fit for pmDE

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.

q_pm_ra : [0.0,9.9] Goodness of fit for pmRA (float)

Goodness of fit for pmRA

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.

pflag : [ PX] mean position flag (string)

[ PX] mean position flag

’ ’ = 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.

posflg : [ DP] type of Tycho-2 solution (string)

[ DP] type of Tycho-2 solution

’ ’ = 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.

ccdm : CCDM component identifier for HIP stars (string)

CCDM component identifier for HIP stars

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.

prox : [3,999] proximity indicator (short, Angle[100mas])

Proximity indicator

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.

bt_mag : [2.183,16.581] Tycho-2 BT magnitude (float, Magnitude[mag])

Tycho-2 BT magnitude

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.

vt_mag : [1.905,15.193] Tycho-2 VT magnitude (float, Magnitude[mag])

Tycho-2 VT magnitude

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.

e_bt_mag : [0.014,1.977] s.e. of BT (float, Magnitude[mag])

s.e. of BT

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.

e_vt_mag : [0.009,1.468] s.e. of VT (float, Magnitude[mag])

s.e. of VT

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.