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U-Band Star Flats » History » Version 1

Gary Bernstein, 07/21/2014 03:23 PM

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h1. U-Band Star Flats
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*21 July 2014 GaryB*
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_Am I seeing CTI problems in the u-band star flats?  Is this an issue for any low-background exposures, including our standards exposures?_
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I am constructing a star flat from the u-band exposures taken by Jonathan Hargis on night of 22 March 2014 (295292-295313).
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Since flat lamps were not working that day, I constructed a u dome flat from 13 July 2014 calibrations biases & domes (335787-335805).  Only departure from standard processing is that I do *not* adjust each CCD to a common mean in the flats.  They are scaled by a single common normalization factor (SCALMEAN).
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Here is the output of the star flat process.  I omitted the central N4/S4 pair (since they have a "bright spot" in u band that will confuse the current issue) and the flaky S7.  Orientation is that N chips are at the bottom, S7 at the right:
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!uAll.png!
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Note that *most of the S chips have gradients along their y axes and the N chips have gradients the other direction.*  These gradients are about 0.1 mag across the device.
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Just for reference, here is what the dome flat looks like (using the "local" scope in ds9 so each CCD has its own zscale).  It does *not* show the gradients in this pattern.
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!uDome.png!