Using VIM

Example 5: Making new columns and plotting with Tomcat

From 594 stars from the Guide Star Catalog, crossmatch with USBO-B, compute colors, and make a 3D plot.

As in Example 2, we start by loading one of the example tables, in this case 594 (essentially) random sources. Choose Load Sky Positions / from link to VOTable , then bring up the examples in a new window, and copy the location of the GSC example. Put that into the box, and click "Get Positions from URL".
You will see the first hundred of the list of 594, the others are all saved in the workbench. You can use Table Columns / sources to see other table columns, for example Fmag and Jmag. You can use Utility / Sex degrees to choose sexagesimal and/or degrees for your positions.
Now let us make a proximity search with anpother catalog. Choose Fetch Data / Proximity Search, then set the radius to be 3 arc-seconds, and the name of the new table is usnob. Select USNO-B from the pulldown, and then start the search. This took nearly four minutes, so please be patient!
When the search is complete, you will see that many of the GSC stars have exactly one match with USNO-B. Choose Table Columns / usnob to view the data from the search. You can see the proximity of the USNO-B source to the GSC entry with the column labeled "Prox[arcsec]".
Now we merge the USNO-B table with the GSC table. Use Mine Data / Merge with Sources and choose the option "best" (i.e. closest), then click "Join to position table".
The position table now has all the columns from USNO-B. Use Table columns / sources to see this, and select for view the magnitudes usnob_R1, usnob_B1,usnob_R2,usnob_B2. The result will have six magnitudes displayed, two from GSC and four from USNO-B.
We can compute colors by subtraction. Choose Mine Data / Compute New Column and make a column FR1 = Fmag - usnob_R1 Similarly make JB1 = Jmag - usnob_B1 and R12 = usnob_R1 - usnob_R2. We can select out the stars where the magnitude is set to 0 or 99 or something else by choosing Mine Data / Select and keeping those with FR1<5 && JB1<5 && R12<5.
Now we can bring the table back to the desktop, and use Topcat to show the plot. Choose Utility / View all files to see the contents of the workbench, then download the file "sources.votable".
Load the table into Topcat, then select the icon for a three-dimensional plat. Choose the three color columns that we computed, FR1, JB1, and R12. Your plot should look a little like this one to the right.