Photometrica - Instant photometry of remote telescope CCD images

Step 5: Importing Comp Stars

Since V Cnc is a AAVSO program star we can save us a lot of work by importing comparison stars directly from the AAVSO comparison star database.

Click the target name link on the File List page to open the image. Click the 'Import Sequence' drop-down list in the menu above the image and select 'AAVSO (online)':

Figure 1: Importing a sequence from the AAVSO

The AAVSO comparison star database is searched using the target name, in this case 'V Cnc'. When the search is completed the results are displayed:

Figure 2: Results from the AAVSO comparison star database (click for larger version)

The list at the bottom of the page is the output from the comparison star database. In our case several comp stars was found. By clicking the 'OK' button we accept all comp stars that has a SNR greater than that specified (100 in this example). Optionally, if no comp stars was found it is possible to search again using a different name.

Also note that Vizier is searched looking for the coordinates of the target star (not comp stars). These coordinates are used to add the target to the analysis (regardless of its SNR).

By clicking 'OK' we return to the image and see something like this:

Figure 3: Image after import

Each comp star measurement now contains BVRI photometry. And of course, one should check that the correct stars has been selected. This is especially important in a crowded field.

Finally, we want to use star '131' as a check star, so we move the mouse over its aperture and change the type in the info window. This is what it finally looks like:

Figure 4: Adding a check star

Target stars are green, comp stars blue and check stars orange.

Next: Inspecting the measurements