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Star alignment problem with JWST images of NGC 2070

Processing Deep Sky NGC2070 NGC Objects
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George Hatfield avatar
George Hatfield avatar
I'm working on the NGC 2070 image from JWST. No problem with the download. However, I can't seem to get the different filter images to align in Pixinsight. This is evident when I look at the combined image (090B, 200G, and 470R). When I look at a bright star on the left side of my image (see below), it is obvious that the blue channel is not aligned with the other two. The problem is not consistent over the entire image. The center, for example, is fine. The upper right is misaligned, but the lower right seems OK. Things I've tried.

1.  The images are different in size.  Resampled to approximately the same size.  No improvement
2.  Tried using a different filter to align to (e.g., rather than 090, used 200).  No improvement
3.  Tried thin spline.  No improvement

Suggestions?

Thanks in advance,  George


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andrea tasselli avatar
andrea tasselli avatar
Try 4th order splines or even 5th or 6th.
George Hatfield avatar
George Hatfield avatar
Thanks, Andrea.   I tried 6th order, no help.  I think I need a distortion model which is way above my "paygrade."

George
George Hatfield avatar
George Hatfield avatar
If anyone would like to try aligning these files, I have posted them on Dropbox.  George

https://www.dropbox.com/scl/fo/wp6z4ryh52l7sxtjqp132/AC7tjL_9kVOMu_eLQROKOfc?rlkey=c7roteynqdn1qxbkz50vt2qwc&st=eyhhde2v&dl=0
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Brian Puhl avatar
Brian Puhl avatar
It looks to me the problem isn't in your alignment.  It's working fine.   The problem was in the original stack.    The 470 data already has quite a few double stars on the top left of the frame, registration didn't work.   It needs to be restacked.  

Brian Puhl avatar
Brian Puhl avatar
Hell, they all have registration and rejection issues.
George Hatfield avatar
George Hatfield avatar
Yes, these masters do have issues.  I'm not sure they are stacking issues since I read somewhere that these images are not the usual stacked masters in the earthly sense.  However, they are often mosaics of smaller images, which can lead to defects.  However, the NASA-processed image shows that a decent result is possible.  See below for my partially processed image vs the published NASA image.   Given the color similarities, I suspect the same masters were used.  But who knows?  Maybe they had access to the pre-mosaic images.  Also, NASA undoubtedly has access to processing techniques we can only dream of.  I think I will give up on this one and move on.  

George
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andrea tasselli avatar
andrea tasselli avatar
Where are the unstacked images?
George Hatfield avatar
George Hatfield avatar
I don't think they are available to the public.  Here is one of the better descriptions of JWST image preparation.

https://esawebb.org/about/general/image-processing/#:~:text=The%20frames%20are%20stacked%20and,perceptibly%20move%20during%20an%20exposure.

George
George Hatfield avatar
George Hatfield avatar
Correction, the individual images are available (https://mast.stsci.edu/search/ui/#/jwst), but the complexity, at least for me, is overwhelming.

George