Troubleshooting guide

root = ugc3371.j Root infile name?
First = 21 First image in set?
Last = 25 Last image in set?
(telesco= KPNO2.1m) Telescope(MMT, Mayall, KPNO2.1m)?
(mode = q)
• fwscan takes a range of images as inputs, in the form
fwscan <image root name> <First image number> <Last image number>
It computes running difference images from which it computes the FWHM. You can use this to
monitor the seeing during a sequence of observations. To use this for focus runs, e.g.,
• 2mguest@flmn-2m-1a{17} singleimage.pl
• 2mguest@flmn-2m-1a{18} relative.offset.kpno.pl 10 0
• Increment the focus (typically 50 – 100 units).
Repeat these three steps as necessary, offsetting the telescope back and forth between each image.
Once you've taken 2 or more images epar fwscan to make certain it is set up for the 2.1-m, then run
fwscan. Here's some sample output:
fl> fwscan ros25h 1 9
#Main Bkgd 1st
#Frame Frame Average Median Quartile #stars
1 2 1.49" 1.48" 1.34" 235
2 1 1.37" 1.37" 1.25" 213
3 2 1.40" 1.39" 1.30" 189
4 3 1.67" 1.67" 1.51" 205
5 4 1.49" 1.48" 1.31" 201
6 5 1.55" 1.56" 1.44" 146
7 6 1.43" 1.42" 1.26" 152
8 7 1.39" 1.39" 1.31" 97
9 8 1.56" 1.55" 1.43" 84
• fwcheck differences only two frames, computes the FWHM, displays the difference frame in buffer 4
of ds9, and finishes with an imexam cursor on the image. To call it:
fwcheck <image root name> <background image number> <source image number>
• Some notes on using imexam, in the standard manner:
• After an image has displayed in ds9 type imexam with no arguments at the cl> prompt
2
. You can keep
imexam open as you continue to take focus images.
• Use the r, a, and e keys to obtain information on the image quality.
• We usually use the Moffat fit number (the second fit number from the right after hitting the a or r
keys) for characterizing the image quality.
• FWHM of 2 – 2.5 pixels over the entire chip are respectable (1.2 – 1.5 arcsec).
• Optimize focus on stars out about 350-500 pixels in radius from the center of the chip.
• Stay away from the left edge, however, as it is slightly more out of focus than the rest of the array.
2 Note that if you type in the image name, IRAF will have to redisplay the image and possibly will not choose a useful
image scaling; it will also disable the scaling buttons in ds9. It is generally better to use the ds9 File/Open menu in order
to display an image rather than type display in IRAF.
FLAMINGOS@2.1-m, Ver. 2.39, 2011 May 13 Page 17 of 46