Photometrica - Instant photometry of remote telescope CCD images

Step 8: Results

With all necessary measurements added and verified, it is time to measure the brightness of the target. We use the comp stars and check star as defined in Step 5: Importing Comp Stars. Click the 'Done!' button in the toolbar above the image:

Figure 1: Get the results

The results page will be displayed:

Figure 2: Results for V Cnc (click for larger image)

The top table lists the estimated magnitude for all target and check star. The check star is displayed in gray, with its known magnitude behind the name of the star:

Figure 3: Magnitude estimates of targets and check stars

The magnitude estimate is the average of the estimate given from each individual comp star. You can also click on the star name to see the details for that star (Step 6: Inspecting Measurements).

The table also lists an error estimate, SE, which is calculated from the SNR. It includes both the target and all comp stars (root of squared errors), and is ready for reporting. Experience has shown that this often under-estimates the error. As an alternative, a standard deviation is also given. This is simply the standard deviation based on each individual comp stars magnitude estimate. If several comp stars are used (three or more) this should be the error reported. This is what Photometrica does in the AAVSO report (see below).

Furthermore, the result page list some essential information pertaining to the image, such as JD of the observation, air mass, exposure time etc.:

Figure 4: Image summary

And finally, essential information of all comp stars including BVRI data are listed in the table at the bottom of the page:

Figure 5: Comparison star table (click for larger image)

Quite a lot can be done with this list. If you prefer, BVRI data can be entered here instead of when the measurement is added to the image. Also, you can disable stars by removing the check in the 'Active' column. To update the analysis to reflect such changes, click the 'Refresh Analysis' link:

Figure 6: Modify comp stars and refresh the results

You can also export the comp star data to Excel or to a tab delimited text file for further analysis. It is also possible to create an AAVSO extended format file that can be uploaded to AAVSO. Since V Cnc is an AAVSO program star, we will do this, and start by clicking the 'Create AAVSO Report' link above the list:

Figure 7: Create the AAVSO report

The next page asks you to enter your observer code. What you enter will be stored in a cookie and used next time you create a report. The other fields are filled with default values and should be OK to use. The 'Notes' field contains the name of the system used, but you can add more information if you like.

Figure 8: Enter data and download file

If you have not supplied proper star names yet you should do it now. The target star name must be recognized by AAVSO and the comp stars should have names as given on the chart. If you have followed the standard way of doing things (as described in this tutorial) everything should be OK and you simply click the 'Create Report File' to download the report.

The report is a simple text file that you store on your computer. To complete the observation you have to go to the AAVSO web site, log on to WebObs and upload the file.