Twilight sky flats with Keplercam.

Created: 04/02/03 by EF
Updated: 10/25/10 by EF

The script kdotwilight.script allows one to create sky flats automatically with Keplercam. The script determines the date of observation and calculates the appropriate exposure times, given the readout time of Keplercam.

The script determines which filter is in place and uses it to expose. It may be used with any filter, but it is the only useful means to obtain U flats, because the output of the lamps is insufficient at the shortest wavelengths.

The script generates files named "X.FLATSkyY.fits," where X is the CCD sequence number and Y the first character in the name of your filter.

The script takes the exposures for you, starting where the telescope was pointed initially (preferably near zenith). NOTE: the script may be used at dusk or dawn. The calculation of exposure times is based on the algorithm of Tyson and Gal (1993 AJ, 105:1206).

Before running the script, you need to determine an exposure time T that yields 10-12K counts on average. You might do this by trial and error at the beginning or end of your first night. Once you have determined T, in the telshell, type "kskyflat", an alias to "source /home/observer/scripts/kdotwilight.script".

The script will prompt you for the number of exposures you desire, the initial exposure T and the binning you are using. It will then start a sequence of exposures and offset the pointing 50 arcsec W between each exposure. It should maintain an average of 10-12K counts in each exposure.

The new Telshell command "Rskies" uses a different algorithm that seems to maintain constant count levels better than ktwflat. It is implemented only for the u band so far. If you wish to try it, please experiment and let us know. It has a companion script that calculates the time to start the flats. In Telshell, type "Rskytime" to see when you can start your sky flats (at dusk or dawn).

If you have any comments, please send email to E. Falco and be as specific as possible.