Fringe removal
Francisco Valdes wrote on Jan 13, 2010
From: Haw J Cheng <hawcheng@physics.unc.edu ([email]hawcheng@physics.unc.edu[/email])>
Date: January 13, 2010 3:21:13 PM MST
To: fvaldes@noao.edu ([email]fvaldes@noao.edu[/email])
Subject: Fringing
Frank,
Hello. I'm an astronomy graduate student at UNC in Chapel Hill. I work with Bruce Carney (if you know who that is.) I am working on images of some I band images of dwarf galaxies and am experiencing some difficulty in defringing them.
I want to experiment with creating my own fringe frame, but am having difficulty finding any good recipes or documentation on the web. I saw that answered a lot of posts concerning fringing on iraf.net, so I thought I would ask you. If you could point me to the right place it would be much appreciated.
Thank you for your time.
Haw Cheng
From: Frank Valdes <valdes@noao.edu ([email]valdes@noao.edu[/email])>
Date: January 13, 2010 4:42:27 PM MST
To: Haw J Cheng <hawcheng@physics.unc.edu ([email]hawcheng@physics.unc.edu[/email])>
Subject: Re: Fringing
Hello Haw,
Yes I know Bruce.
The best general guide I can think of is the one developed for reducing mosaic data for the NDWF survey. While this is written for mosaic data (multiple CCDs in an exposure) the discussion and tools are generally applicable in most cases to single CCD images.  The link is below and the part on fringing is in the "towards a more perfect flat field" section.
http://www.noao.edu/noao/noaodeep/ReductionOpt/frames.html
Basically the method requires you to create a "dark sky flat field" by stacking sparse dithered exposures to reject sources. If you do not have exposures without the galaxies or with sufficient dithering to avoid lots of overlap then you will have difficulties. The stacking is handled ultimately by IMCOMBINE or related task. Then some filter is run over the image to remove the lower frequency background by subtraction. This leaves a "fringe frame". The final step is scaling and subtracting this from the science exposures to best remove it. For a small amount of data this might be best accomplished interactively with a display. The quality of the subtraction would be determined by looking at regions of blank sky around the galaxies of interest.
I hope this help.
Yours,
Frank Valdes
Post generated using Mail2Forum (http://www.mail2forum.com)
Date: January 13, 2010 3:21:13 PM MST
To: fvaldes@noao.edu ([email]fvaldes@noao.edu[/email])
Subject: Fringing
Frank,
Hello. I'm an astronomy graduate student at UNC in Chapel Hill. I work with Bruce Carney (if you know who that is.) I am working on images of some I band images of dwarf galaxies and am experiencing some difficulty in defringing them.
I want to experiment with creating my own fringe frame, but am having difficulty finding any good recipes or documentation on the web. I saw that answered a lot of posts concerning fringing on iraf.net, so I thought I would ask you. If you could point me to the right place it would be much appreciated.
Thank you for your time.
Haw Cheng
From: Frank Valdes <valdes@noao.edu ([email]valdes@noao.edu[/email])>
Date: January 13, 2010 4:42:27 PM MST
To: Haw J Cheng <hawcheng@physics.unc.edu ([email]hawcheng@physics.unc.edu[/email])>
Subject: Re: Fringing
Hello Haw,
Yes I know Bruce.
The best general guide I can think of is the one developed for reducing mosaic data for the NDWF survey. While this is written for mosaic data (multiple CCDs in an exposure) the discussion and tools are generally applicable in most cases to single CCD images.  The link is below and the part on fringing is in the "towards a more perfect flat field" section.
http://www.noao.edu/noao/noaodeep/ReductionOpt/frames.html
Basically the method requires you to create a "dark sky flat field" by stacking sparse dithered exposures to reject sources. If you do not have exposures without the galaxies or with sufficient dithering to avoid lots of overlap then you will have difficulties. The stacking is handled ultimately by IMCOMBINE or related task. Then some filter is run over the image to remove the lower frequency background by subtraction. This leaves a "fringe frame". The final step is scaling and subtracting this from the science exposures to best remove it. For a small amount of data this might be best accomplished interactively with a display. The quality of the subtraction would be determined by looking at regions of blank sky around the galaxies of interest.
I hope this help.
Yours,
Frank Valdes
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Last post on Jan 13, 2010