Cross-match using TopCat

You can send tables to TopCat from your VOSpace, if you have the AstroGrid Desktop running, or upload them from your local disk. TopCat provides many tools including an internal crossmatcher (one 'match') or a crossmatcher for more than one table (two 'matches', as illustrated). The embedded help or TopCat home page describe all the options.

• NB If your input tables are in different coordinates, e.g. degrees v. hours of RA, that is OK. If they are in different Equinox systems e.g. B1950 v. J2000, or Galactic v. Equatorial, you can convert them first using the TopCat functions.

• You could choose a variety of Sky position-based matches, and chose whether to select all or only the best matches, within an error circle, etc.

• This shows selecting data around Orion KL from IRAS and 2MASS using the VO Desktop, sending the tables to TopCat and matching on position with a 30-arcsec error radius, passing all matches.

• You can match on any columns, for example offsets in Cartesian coordinates (x, y) with velocity as a third axis, and perform on-the-fly mathematical operations.