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The way you will be removing the bias and flat field effects is by  using the IRAF procedure {\tt ccdproc}. We first need to load some IRAF packages. Type:  {\color{red}  \begin{verbatim}  cl> noao  cl> imred  cl> ccdred  \end{verbatim} \end{verbatim}}  Before we do anything, we need to set the parameters of ccdproc, so  that it will do what we want. To do this, type {\tt epar ccdproc}