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
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.|