Library Fringe Frames
For each WFS run on the INT a series of library fringe frames are being
constructed for any R (see note at bottom of page), I, i', or Z-band data
taken. As expected filters blueward of R show no measurable fringe patterns.
WFS runs using the SDSS r' filter show no measurable sky fringes,
highlighting the pitfalls caused by the extended the red tail of the
conventional "Harris" R-band filter.
Using the red filters results in the following fringing levels - for reference
rms dark sky photon noise is approximately 1% of sky for a 600s exposure.
- The Harris R-band filter shows low level fringing at
+/-0.5% of sky
- The I-band filter has modest fringing at +/-3% of sky
- The Z-band filter has severe fringing at +/-6% of sky
- The r'-band SDSS filter shows no sky fringing
- The i'-band SDSS filter has fringing at +/-2% of sky, noticeably less
than the I-band filter.
- The SDSS g' filter suffers from optical quality problems over
small areas.
After optimally removing the zeroth order fringes the residual fringe
pattern is generally < 1/10th of the original level. In particular the
results so far indicate that:
- for the Harris R-band filter the defringed frames have
negligible, < 0.1% of sky, residual fringes
- for the Iand i'-band filters, residual fringe patterns are still visible\ at
a level of order 0.2% of sky
- for the Z-band filter, residual fringes at a level of 0.4% of sky
are still visible
Zeroth order fringe removal has been done for all R, I, i' and
Z-band data taken and processed throught the WFS pipeline (from more details
click here ).
The master zeroth order fringe frames (or sky super flats if you prefer that
term) were constructed using imcombine within IRAF to produce a nightly
stacked image for each passband. Each of the nights was them imcombined
to produce the "average" or zeroth order fringe frame for each separate
observing run. Examples of these are accessible below.
The simplest way to access a file is to select the appropriate month/year,
click on the link to obtain a listing of available files, and then right click
to download the file.
WFS fringe maps are now available on
flatsnbiases page
For examples of other fringe frames contact mike@ast.cam.ac.uk.
