Extragalactic Reference Link Catalog (ERLcat )

Last update: 2004 July 30, Norbert Zacharias, nz@usno.navy.mil

Corrected version

The original version of the ERLcat data has been replaced by this
corrected version on 2004, July 30. The individual fields epoch
and field name were offset by 1 line in the original version.
Thanks to Olexander Daniltsev, Kiev, who pointed out this mistake.
Thanks to Gary Wycoff, who created the corrected files.
The new data now include also the epoch for each star and the telescope
identification, appended to each position line, not just in the
cross-reference table. Thus the new files adopt the format of the
ERLcat at the CDS (I/273).
The new version contains the same number of stars with the same positions.


This is an astrometric catalog, providing positions of 89,422 stars
in 398 selected fields of extragalactic reference frame sources.
The stars are mainly in the 11 to 14 magnitude range.
The average positional accuracy is about 50 mas per coordinate
at the epoch of observation, which is between 1976.2 and 1991.9.

Observations are based on photographic plates, taken with 2 telescopes:

To get the data

See the table of contents and select specific fields:
after retrieval, save to a file locally if you like.

Get the entire catalog file:
All fields are on 1 file (ASCII, ftp, gzip).

Optionally, get a Fortran program to be used with the entire catalog file,
to extract selected fields locally.
Save to a file on your system, edit path names, compile and run.


The catalog is described in a paper submitted to AJ (de Vegt et al.).

The format is as follows:

      star  mag         RA         DC  sx  sy np   box   epoch   tID 
 117800037 1327    8616042   61767911  52  58  4 M0Y134H 1993.7979 Z
 117800045 1318    9500876   61342459  87  71  4 M0Y134H 1993.7979 Z
 117800049 1298    8005086   62095177  90  64  4 M0Y134H 1993.7979 Z
 117800069 1147    8251601   62808431  52  52  4 M0Y134H 1993.7979 Z
 117800083 1110    8722658   62115527  85  65  4 M0Y134H 1993.7979 Z

  column  format  unit   explanation
  star     I10         star number 
  mag      I5   1/100  catalog magnitude 
  RA       I11   mas   right ascension 
  DC       I11   mas   declination
  sx       I4    mas   formal error RA * cos(DC) 
  sy       I4    mas   formal error DC  
  np       I3          number of plates used 
  box    1X,A7         name of box (field) 
  epoch   F10.4  year  observing epoch of position
  tID    1X,A1         telescope ID (Z or B)
For several fields, multiple files (boxes) are provided.
These are observations of the same field made with different 
telescopes and/or at widely separated epochs.

The coordinates are on the Hipparcos System, thus on the ICRS,
which is consistent with the J2000 coordinate system.  The
positions are given for the indicated observing epoch.

Telescope ID: 
Z = Hamburg Zone astrograph, Germany
B = Black Birch astrograph (USNO, New Zealand)