Subject: NIC-FPS information - upcoming users please read!

From: Suzanne Hawley

Submitted: Mon, 5 Nov 2007 16:50:13 -0800 (PST)

Message number: 1070 (previous: 1069, next: 1071 up: Index)

5 November 2007

Dear APO 3.5m NIC-FPS users,

     NIC-FPS is currently back in operation in imaging mode but is still 
undergoing engineering testing to address two noise issues - higher than 
expected readnoise in the normal images, and an intermittent noise problem 
that manifests itself as a rapidly rising background level.  It is usable 
for science operations with the following recommended procedures (which 
differ somewhat from what is described in the manual).  Note that the 
Fabry-Perot etalon mode is still in commissioning and is not yet available 
for science operations. We will update you as the instrument status 
progresses on both imaging and etalon modes.

Recommended NIC-FPS observing procedure (starting in November, 2007)

1. All science images should be taken with Fowler sampling set to FS=8. 
This will cut down the readnoise in the images as much as possible.  With 
FS=8, the typical noise levels are comparable to what were previously seen 
with NIC-FPS. A higher number of Fowler samples is not presently 
available, so do not try to set FS > 8.

2. Two fits files are now written for each exposure.  The first, called 
(name).fits goes to the usual /export/images directory and contains two 
images (fits files extensions [0] and [1]). The [0] extension is a 
fully-processed image using all sixteen of the chip reads that are 
performed with FS=8.  This is the science image, and should be sufficient 
for nearly all purposes.  The [1] extension is the raw image of the last 
chip read, and can be used to check for saturation, sky background, etc.

The second fits file that is written is a raw fits file with information 
from all 16 reads for FS=8.  These files are very large (more than 30 Mb) 
and it is untenable to transport them quickly across the network for 
remote observing. Therefore, they are saved as (name).raw.fits files, and 
planned to be made available in the usual /export/images directory in the 
future.  At present they are being written to the instrument computer and 
are not easily accessible. You should only need these if some issue arises 
with the normal (name).fits file - in this case contact the APO staff 
after your run and we will work with you to get the data you need.

3. Darks (mask in place) should be taken with the same exposure time as 
each of the science exposures.  Darks should also be taken with FS=8 to 
reduce the readnoise.

4. The Observing Specialist will be monitoring the background levels using 
zero second FS=0 darks.  These should show mean background counts of 3000 
+/- 1000 with the mask in place.  If the background begins to rise 
rapidly, the Observing Specialist will need to do some instrument resets 
which may take 5-10 minutes.  Please be patient during the monitoring, and 
if needed resetting, process.

Adam Ginsburg and Corey Wood
NIC-FPS instrument team
University of Colorado

Suzanne Hawley
Director, ARC 3.5m Telescope
Apache Point Observatory


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