Select WDS Catalog

Name: Select WDS Catalog (19k)
Contributor: Ellsworth G Dutton (
Date submitted: Oct 15th, 2003


This catalog is intended to provide a subset of of the Washington Catalog of Double Stars (WDS)  that might be more interesting to view in a telescope because selected pairs are relatively close together and have similar magnitudes.  All information for each pair is taken from the WDS with a Difficulty Index (DI) added to indicate how difficult it is to split the pair, DI of 100 being the hardest and 1 being the easiest. The DIs in this catalog range from 92.47 to 32.06.  The DI is determined from a freeware program discussed in Sky & Telescope, Jan 2002.

Note that the SelectWDS catalog uses the J2000.0 coordinates from WDS that are only given to the nearest 0.1 min. in RA and 1.0 min in Dec so they are not plotted as accurately as the standard (Tycho-II) Skymap catalogs for the pair.  The SelectWDS objects are plotted as a green circle and three sides of a square within that circle.

The 522 doubles in this example catalog were selected  according to the following criteria:

a) Magnitude of primary  --    brighter than mag 8
b) Max magnitude difference    --   2.0
c) Min separation   --         1.2 arc seconds
d) Max Separation     --     5.0 arc seconds

The separation value used in the last observed value given in the WDS, the date of that observation is given in SelectWDS Other subsetted WDS catalogs for Skymap, .dat and .sdd files, using selection criteria customized to individual requests are available (on a limited basis) from Ells Dutton, )

There are general limitations on the computation of the Difficulty Index using the algorithm supplied in the 2002 S& T article:
a)  Magnitude of secondary must be brighter than mag 10
b) Current separation (last date observed in WDS) must be greater than
1" and less than 10"