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The original GMOS-N EEV CCDs had significant fringing in the red. The new E2V DD CCDs have much weaker fringing. This page shows examples of fringe frames in imaging mode from both arrays in the i'-filter and the z'-filter.
More recent fringe frames for both i' and z' are available from the Gemini Science Archive. To retrieve either the raw or the processed frames one can follow eg. these steps (Note that the new DD E2V CCDs were installed Nov 2011):
- Under GSA Queries select menu item Search Complete Catalogue
- Select a Standard Query GMOS-N and/or GMOS-S and click Continue to query form...
- In Target Name enter Fringe
- From the Resolver: menu select Gemini name (not the default value SIMBAD/NED)
- in Filters enter either i_G0302 or z_G0304
- From the Instrument menu select GMOS-N
- In CCDSUM enter either 1 1 or 2 2
- Select the raw or processed frames you wish to retrieve and continue by clicking Download Datasets. Note the processed frames have _fringe in the Data Label and the filename begins with RG.
The original EEV CCDs
The data shown for the original EEV CCDs were obtained the night of August 19-20, 2001, during the commissioning of GMOS-N. This was close to new moon, and the sky was photometric. The fringe strength in the z'-filter is typically +-2.5% of the background, while in the i'-filter the fringing is +-0.7% of the background.
z'-filter fringe frame.
i'-filter fringe frame. The images was median filtered with a box 17pixels by 17 pixels in order to increase the signal-to-noise. Because this fringe frame was constructed from only 6 science exposures, artifacts are seen from insufficient cleaning of signal from objects. The signal in the artifacts is typically less than 1% of the background level.
Relative strength of the fringes in the z'- and the i'-filter.
z'-filter science frame before and after fringe subtraction.
i'-filter science frame before and after fringe subtraction.
The data shown for the new E2V DD CCDs were taken between Dec 2011 - Feb 2012, on photometric nights in dark time. Fringing in the z'-filter is typically +-0.3% of the background, while the i'-filter fringing is less than +- 0.15% of the background.
z'-filter fringe frame.
i'-filter fringe frame, median filtered with a box 17 pixels by 17 pixels in order to increase the signal-to-noise to make the fringes more apparent.
A z'-band science frame without fringe subtraction. Note the fringing is much weaker than in the original EEV CCDs as shown above.
A comparison of z'-band fringing between the original and upgraded EEV CCDs:
This shows a cut along a single column. Fringing in the new DD E2V CCDs in the z'-band is about a tenth as strong as in the original EEV CCDs.