Photometrica - Instant photometry of remote telescope CCD images

Step 6: Inspecting the Measurements

Often one wants to take a closer look at the stars to check that they are not over-exposed, does not contain a cosmic ray hit, hot/cold pixels or other artifacts. Although a lot can be seen directly in the image, Photometrica offers several ways to inspect the details of a measurement.

First of all, lets check to see that the stars are not over-exposed. Move the mouse pointer over the aperture of each star to display the information window. Check the value of the 'Max' field:

Figure 1: Max ADU

This value is the maximum ADU value for any one pixel inside the aperture. A common rule of thumb is to keep this value below half of maximum possible ADU (32 768 for 16 bit cameras). Experience has shown that one is save up to at least 45 000 for the GRAS systems. Next, click the 'More ...' link:

Figure 2: How to get to the details page

This will take you to the details page for that measurement. It contains all available information, as well as some diagnostic plots:

Figure 3: Details page (click for larger image)

At the bottom of the page you will find the ADU readings in tabular form. It easily reveals cosmic rays, hot/cold pixels and other artifacts, close companion stars etc.

Figure 4: ADU readings

A similar way to view this data is the 3-D plot. Click the link under the image at the top of the page (the same link is available from the pop-up dialog in the image):

Figure 5: 3-D view of star image

The 3-D view can be rotated in any direction.

Next: Choosing Aperture Size