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gaia early data release 3 documentation

12.2 External catalogues

12.2.1 tycho2tdsc_merge

Tycho-2 merged with the TDSC catalog and TDSC supplement.
The Tycho Double Star Catalogue, (TDSC, Fabricius et al. 2002) contains 98482 components of double and multiple systems processed in the Tycho-2 context. It includes either original Tycho-2 data or results from a dedicated re-processing aimed at binaries. As pointed out by P. Marrese (personal communication), the TDSC star with identifier 29583 is redundant and it was therefore skipped. The TDSC supplement contains data from an additional 4777 components from either Hipparcos or Tycho-1.
The Tycho-2 main catalogue (Høg et al. 2000) contains 2 539 913 sources, including many binaries, but a minimum separation of 0.8 arcsec was imposed during the catalogue construction. The Tycho-2 supplement-1 contains data for 17588 Hipparcos and Tycho-1 stars, which do not appear in the main catalogue, but only the 4777 stars relevant for TDSC are included here. The Tycho-2 supplement-2 contains an additional 1146 Tycho-1 stars of poor quality.
We have merged Tycho-2 (main) with the TDSC main and supplement, keeping the Tycho-2 data model and extending it to include TDSC–specific fields. This is only possible to a certain degree as specified in detail below. In particular, Tycho-2 includes fields for mean position, proper motion etc. for a combination of Tycho-2 and several ground based catalogues. These fields are inherited for TDSC main stars, but were not derived for the TDSC supplement, where we only provide HIP proper motions. For Tycho-2 stars not in TDSC, blank TDSC fields were appended.
For Tycho-2 stars in TDSC, the following fields were replaced by the corresponding TDSC fields:

  • tyc1, tyc2, tyc3;

  • hip;

  • ccdm.


In addition, if the TDSC contains a new solution:

  • bt_mag, e_bt_mag, vt_mag, e_vt_mag, ra_deg, de_deg, ep_ra1990, ep_de1990, e_ra_deg, eDeDec;

  • The mean position flag, pflag, is set to ‘P’ (“photocentre”) if resolved and there are Tycho-2 mean positions. Mean position etc. are then repeated for both new components;

  • The proximity indicator, prox, is set to blank if the Tycho-2 star was resolved in TDSC;

  • The type-of-solution flag, posflg, set to ‘N’;

  • For resolved Tycho-2 stars, two records are given.


For the few TDSC stars with new solutions, but not in Tycho-2, and for the TDSC supplement stars (Hipparcos or Tycho-1), the Tycho-2 part of the merged record was populated in the following way:

  • TYC1..3 from TDSC;

  • pflag set to TDSC pmflg (‘H’ or ‘X’), ‘H’ indicating Hip proper motions;

  • no mean position and related fields;

  • proper motions only for Hipparcos stars;

  • BT,VT photometry from TDSC;

  • Tycho-1 flag, tyc, is set to posflg, i.e. ‘T’ or ‘H’ although Hipparcos stars may well be in Tycho-1;

  • Hipparcos, hip, and CCDM, ccdm, identifiers from TDSC;

  • astrometry from TDSC, but the (ra, dec)-correlation, corr, is set to blank.


New TDSC specific fields added after the Tycho-2 part of the record:

  • sys_no, cmp, n_main, n_sup, magflg, wds, note, hd;

  • rcmp, pa, sep, e_pa, e_pa_sep, e_sep.

Columns description:

id : Tycho-2 identifier (string)

The Tycho-2 identifier id string TYC … 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 component identifier (tyc3) for TDSC entries is copied from TDSC. The recommended star designation contains a hyphen between the TYC numbers, e.g. TYC 1-13-1.

hip : Hipparcos number (int)

Hipparcos number identifier.

tyc1 : TYC1 component from TYC or GSC (string)

The TYC identifier string component tyc1) is constructed from the Guide Star Catalogue region number.

tyc2 : TYC2 component from TYC or GSC (string)

The TYC identifier string component tyc2 is constructed from the running number within the tyc1 region.

tyc3 : TYC3 component from TYC or TDSC (string)

The TYC identifier string component tyc3 is normally 1. Some non-GSC running numbers were constructed for the first Tycho Catalogue and for Tycho-2. The component identifier for Tycho Double Star Catalogue (TDSC, Fabricius et al. 2002) entries is copied from TDSC.

id_tycho : Numeric Tycho-2 identifier (long)

These are the IDs as published in Tycho-2. In Tycho-2 objects were identified by 3 numbers (tyc1, tyc2 and tyc3) and we have combined these into a single unique number given by (tyc1*1000000)+(tyc2*10)+(tyc3).

tyc : Tycho-1 star (string)

This field is specific to Tycho-2 and not found in the Tycho Double Star Catalogue (TDSC, Fabricius et al. 2002).

  • ‘ ’ indicates no Tycho-1 star was found within 0.8 arcsec (quality 1-8) or 2.4 arcsec (quality 9);

  • ‘T’ indicates 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.

  • ‘H’ TDSC star not in Tycho-2 but in Hipparcos. It may also be in Tycho-1.

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

Observed Tycho-2 Right Ascension, ICRS. This field is a convenience copy of ra_deg.

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

Observed Tycho-2 Declination, ICRS. This field is a convenience copy of the field de_deg.

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 Ascension, ICRS, epoch=J2000 (double, Angle[deg])

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. Tycho-2 is one of the several catalogues used to determine the mean position and proper motion. The Tycho Double Star Catalogue (TDSC, Fabricius et al. 2002) was not used when forming these mean positions. The observed Tycho-2 position is given in the fields RAdeg and DEdeg.

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

Mean Declination, 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 Tycho Double Star Catalogue (TDSC, Fabricius et al. 2002) was not used when forming these mean positions. 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])

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])

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

ep_ra1990 : Epoch–1990 of ra_deg (float, Time[year])

Epoch–1990 of ra_deg.

ep_de1990 : Epoch–1990 of de_deg (float, Time[year])

Epoch–1990 of de_deg.

ep_ra_m : Mean epoch of RA. (float, Time[year])

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

ep_de_m : Mean epoch of Dec. (float, Time[year])

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

num : Number of positions used for forming mean data (short)

Number of positions used in constructing the mean positions and proper motions, one of these contributing positions coming from Tycho-2.

e_ra_deg : Uncertainty RA*cos(dec), of observed Tycho-2 RA. (double, Angle[mas])

Uncertainty, σαcosδ, of the observed Tycho-2 RA. The errors are based on error models.

e_de_deg : Uncertainty of observed Tycho-2 Dec. (double, Angle[mas])

Uncertainty of the observed Tycho-2 declination. The errors are based on error models.

corr : Correlation (RAdeg,DEdeg) (double)

Correlation (ra_deg, de_deg). For Tycho Double Star Catalogue (TDSC, Fabricius et al. 2002) stars not in Tycho-2, the field is blank.

e_ra_mdeg : Uncertainty RA*cos(dec),at mean epoch. (double, Angle[mas])

Uncertainty, σαcosδ, for the right ascension direction at mean epoch. The errors are based on error models.

e_de_mdeg : Uncertainty of Dec at mean epoch. (double, Angle[mas])

Uncertainty, σδ, for the declination at mean epoch. The errors are based on error models.

e_pm_ra : Uncertainty proper motion in RA*cos(dec). (float, Angular Velocity[mas/year])

Uncertainty, σμαcosδ, for the proper motion in right ascension direction. The errors are based on error models.

e_pm_de : Uncertainty of proper motion in Dec. (float, Angular Velocity[mas/year])

Uncertainty, σμδ, for the proper motion in declination. The errors are based on error models.

q_ra_mdeg : Goodness of fit for mean RA (float)

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 : Goodness of fit for mean Dec (float)

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 : Goodness of fit for pm_de (float)

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 : Goodness of fit for pm_ra (float)

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 : Mean position flag (string)

The mean position flag takes one of:

  • ‘ ’:

    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. It is also used for Tycho-2 stars resolved in the Tycho Double Star Catalogue (TDSC, Fabricius et al. 2002) and the mean positions and proper motions are then repeated;

  • ‘X’:

    no mean position, no proper motion;

  • ‘H’:

    no mean position, but proper motions from Hipparcos. This option is only used for TDSC stars not in Tycho-2.

posflg : Type of Tycho-2 solution (string)

The type of Tycho-2 solution takes one of:

  • ‘ ’:

    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.

Specific values for entries from the Tycho Double Star Catalogue (TDSC, Fabricius et al. 2002):

  • ‘N’:

    New double star treatment for TDSC;

  • ‘T’:

    Tycho-1 position from the Tycho-2 Supplement_1;

  • H’:

    Hipparcos position from the Tycho-2 Supplement_1.

The values [TH] are only used in the TDSC supplement. In the TDSC main catalogue only flags [‘ ’N] are used.

ccdm : CCDM component identifier for HIP stars (string)

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.

For Tycho Double Star Catalogue (TDSC, Fabricius et al. 2002) entries, the HIP and CCDM fields are from TDSC. There, the separation limit of 0.8 arcsec does not applied.

prox : Proximity indicator (short, Angle[100mas])

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.

This is a Tycho-2 specific field. For Tycho-2 stars resolved in the Tycho Double Star Catalogue (TDSC, Fabricius et al. 2002), the field is blank.

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

Blank when no magnitude is available. Either bt_mag or vt_mag is always given. Approximate Johnson photometry may be obtained as: V=VT-0.090(BT-VT) and B-V=0.850(BT-VT). Consult Section 1.3 of Volume 1 of ESA (1997) for details.

Details for the Tycho Double Star Catalogue (TDSC, Fabricius et al. 2002) photometry are specified in ’magflg’.

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

Blank when no magnitude is available. See the description above for bt_mag for further details.

e_bt_mag : Uncertainty of BT (float, Magnitude[mag])

Uncertainty of bt_mag. Blank when no magnitude is available. See the description above for bt_mag for details of the photometric system.

e_vt_mag : Uncertainty of VT (float, Magnitude[mag])

Uncertainty of vt_mag. Blank when no magnitude is available. See the description above for bt_mag for details of the photometric system.

sys_no : TDSC identifier for the system (int)

Tycho Double Star Catalogue specific field (TDSC, Fabricius et al. 2002).

TDSC identifier for systems appearing in TDSC or its supplement.

cmp : Component designation (string)

Tycho Double Star Catalogue specific field (TDSC, Fabricius et al. 2002) of one or two characters. The TDSC system identifier (sys_no) plus the component designation give an unambiguous identification of the TDSC component. When possible, the component designation is from the Washington Double Star Catalog (WDS, Mason et al. 2001). In cases where a component designation is added to a WDS system, or to a system not in WDS, this was normally done using letters A,B,… according to the VT magnitude. Cases where the designations deviate from the WDS designations in a non-trivial way are explained in the TDSC notes.

n_main : Number of components in TDSC main catalogue (byte)

Tycho Double Star Catalogue specific field (TDSC, Fabricius et al. 2002).

Number of components for this system listed in the TDSC main catalogue. The TDSC main catalogue contains components detected in the Tycho-2 (Høg et al. 2000) processing or in the TDSC processing, while the supplement contains components copied across from the Tycho-2 Supplement. A system in TDSC may have components in both the main catalogue and in the supplement. A system known in the Washington Double Star Catalogue (WDS, Mason et al. 2001) may have just one component listed in the TDSC.

n_sup : Number of components in the TDSC supplement (byte)

Tycho Double Star Catalogue specific field (TDSC, Fabricius et al. 2002). Number of components for this system listed in the TDSC supplement (which is included in this merged version). The TDSC main catalogue contains components detected in the Tycho-2 (Høg et al. 2000) processing or in the TDSC processing, while the supplement contains components copied across from the Tycho-2 Supplement. A system in TDSC may have components in both the main catalogue and in the supplement. A system known in the Washington Double Star Catalog (WDS, Mason et al. 2001) may have just one component listed in the TDSC.

magflg : TDSC photometry flag (char)

Tycho Double Star Catalogue specific field (TDSC, Fabricius et al. 2002) giving details for the TDSC photometry.

Except for Hp, the photometry is always on the same system as in Tycho-2 (Høg et al. 2000). We expect the Tycho photometry of Hipparcos stars from Fabricius and Makarov (2000) to be more accurate than the normal Tycho-2 photometry.

  • ‘ ’:

    normal photometry, either from Tycho-2 or the TDSC processing;

  • ‘A’:

    normal photometry given here, but alternative photometry is given in Fabricius and Makarov (2000);

  • ‘F’:

    Tycho photometry from Fabricius and Makarov (2000);

  • ‘T’:

    Tycho photometry from Tycho-1 (ESA 1997);

  • ‘B’:

    BT from Tycho-1, Hp is given instead of VT;

  • ‘V’:

    VT from Tycho-1, no BT;

  • ‘H’:

    Hp is given instead of VT, no BT.

In the main TDSC catalogue only flags [‘ ’A] are used; in the TDSC supplement only flags [FTBVH].

wds : WDS identifier for the system (string)

Tycho Double Star Catalogue specific field (TDSC, Fabricius et al. 2002).

The Washington Double Star Catalogue (WDS, Mason et al. 2001) contains a 10 character field with approximate ICRS coordinates for the primary component in the form hhmmm+ddmm. This field together with the component designation identifies the relevant entries of the WDS. Exceptions and ambiguities are explained in the notes to the TDSC catalogue.

note : TDSC notes (char)

Tycho Double Star Catalogue specific field (TDSC, Fabricius et al. 2002).

Flag for a note, normally to the identification in the Washington Double Star Catalog (WDS, Mason et al. 2001). Some WDS identifications need clarification, e.g. because the WDS entry gives no designation or because the star has more than one WDS designation. In other cases the identification is somewhat uncertain or a new component was added to a known system.

  • ‘ ’:

    no note;

  • ‘A’:

    alternative WDS designation exists;

  • ‘D’:

    dubious/uncertain WDS identification;

  • ‘N’:

    a non-specific note;

  • ‘O’:

    good quality orbit exists, cf. Fabricius et al. (2002), Table 2;

  • ‘R’:

    this WDS component is probably resolved;

  • ‘S’:

    a close companion to a WDS component (probably);

  • ‘T’:

    a Tycho single star, added to a WDS system;

  • ‘U’:

    undesignated in WDS (non-trivial) or unclear designation.

Notes [ANTU] are explained in detail in the file of notes accompanying the original TDSC.

hd : HD identifier for TDSC entries (int)

Tycho Double Star Catalogue specific field (TDSC, Fabricius et al. 2002).

Identifier from the Henry Draper catalogue as listed in the original TDSC catalogue.

rcmp : Reference component for position angle and separation (string)

Tycho Double Star Catalogue specific field (TDSC, Fabricius et al. 2002).

Reference component (cmp) for position angle and separation as detailed in the fields pa and sep.

pa : Position angle (float, Angle[deg])

Tycho Double Star Catalogue specific field (TDSC, Fabricius et al. 2002).

Position angle (degrees) of the present component (cmp) with respect to the reference component (rcmp).

Position angle and separation are computed at the mean observational epoch for the two stars by applying proper motion to the right ascensions and declinations at the individual epochs of observation. The position angle is given relative to the ICRS pole.

sep : Separation (float, Angle[arcsec])

Tycho Double Star Catalogue specific field (TDSC, Fabricius et al. 2002).

Separation (arcseconds) of the present component (cmp) with respect to the reference component (rcmp). See the detailed description for pa for further details.

e_pa : Uncertainty of the position angle (float, Angle[deg])

Tycho Double Star Catalogue specific field (TDSC, Fabricius et al. 2002).

Uncertainty (degrees) of the position angle of the present component (cmp) with respect to the reference component (rcmp).

e_pa_sep : Uncertainty of the position angle * separation (short)

Tycho Double Star Catalogue specific field (TDSC, Fabricius et al. 2002).

Uncertainty (mas) of the position angle, of the present component (cmp) with respect to the reference component (rcmp), multiplied by the separation.

e_sep : Uncertainty of the separation (short, Angle[mas])

Tycho Double Star Catalogue specific field (TDSC, Fabricius et al. 2002).

Uncertainty (mas) of the separation of the present component (cmp) with respect to the reference component (rcmp).