Making a Twilight Flat

There is a handy perl script called makeflat3 that creates a median flat from a list of images. The program automatically normalizes each image from its central subframe to ensure that changing background light levels (due to the darkening of the sky at twilight) do not systematically bias the flat. makeflat3 requires that a median dark image from that day's output is in the current working directory. If a current dark is not present, we can create a pointer to an archived dark. Following the directions here:

NOTE: The instructions for this section need to be checked when we make another flat...I'm not sure which version of makeflat is the one that works!

1. Ensure that a present day 20 s dark is available. If it is not available, either make one as described in Section 7.2 or create a link to an archived dark.

   $ ls /rotse/data/pipeline/cal/               ; Is today's dark there?

   ...

   $ cd /rotse/data/pipeline/cal/

   $ ln -s today_drk0200_3a.fit old_drk0200_3a.fit

   $

2. Check the makeflat3 syntax.

   $ makeflat3

          Usage: makeflat -d flatdir [-f framenum -t datestr -r darkdir -n namestr -c]

3. Run makeflat3 on the data.

   $ makeflat3 -d /rotse/data/pipeline/image/ -t today -r /rotse/data/pipeline/cal/ -n twi

   ...

   This should take a few minutes. Please note the specification of the twi TLA, which is the standard for twilight flats. This should be substituted when running other flats.