plate-solving using known objects

[Laura Watson]

Hi Karen,

Is there a way to plate-solve an image by giving it the designations/coordinates of a couple of known objects in the field?

The problem that I am trying to solve is this: I have an image of an asteroid that contains enough objects to plate solve, but the asteroid is overexposed. I want to apply this result to an image with a shorter exposure, in which the asteroid is not overexposed, but only two or three other objects are visible. Unfortunately there is telescope drift between the images, so I cannot simply keep apply the WCS from the longer exposure to the shorter exposure.

Best,
Laura

[karenacollins]

Hi Laura,

The only thing similar that you can do is set the approximate center of the field using this setting:

Set the radius to be at least the field of view in arcmins.

I expect that will still not help if there are only two or three other visible objects in the field.

Have you tried lowering the noise tolerance to see if the source detection will pick up more faint objects?



If lowering the noise tolerance does find more (valid) sources, I think it would be good to set the "Max Peak" value to something less than the peak value in the asteroid's PSF so that it is ignored (my interpretation is that the asteroid is the brightest source in the field).



If none of the above helps, you could open both the long and short exposure images into an image stack and use the stack aligner () option above the image display to align the images using a single aperture around the brightest common source in both images (other than the asteroid). If the image shift is larger than you can make the aperture, you may have to use "single step" mode to identify the same star with another left-click in the second image.



Then you could copy the first WCS solution to the shorter exposure image.

Karen