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I am trying to remove the sky background from some science spectra using the longslit.background package. I fill in the following inputs into the parameter file

PACKAGE = longslit
TASK = background

input = fncrz0118.HCG40-1219_s3.fits Input images to be background subtracted
output = bfncrz0118.HCG40-1219_s3.fits Output background subtracted images
(axis = 1) Axis along which background is fit and subtracte
(interac= yes) Set fitting parameters interactively?
(sample = 0:85,193:295) Sample of points to use in fit
(naverag= 1) Number of points in sample averaging
(functio= chebyshev) Fitting function
(order = 2) Order of fitting function
(low_rej= 0.) Low rejection in sigma of fit
(high_re= 0.) High rejection in sigma of fit
(niterat= 1) Number of rejection iterations
(grow = 0.) Rejection growing radius
(graphic= stdgraph) Graphics output device
(cursor = ) Graphics cursor input
(mode = ql)

But when I run the task I end up with a black irafterm screen and the following question at the bottom:
fncrz0118.HCG40-1219_s3.fits: Fit line =

I have no idea what this is asking for. I cannot find any information in any of the documentation about this either. Any help is greatly appreciated.

The LONGSLIT.BACKGROUND task is actually the IMRED.GENERIC.BACKGROUND task, which itself is just a wrapper for the IMFIT.FIT1D task which is the thing actually doing the prompt. See the FIT1D help page, especially Example 1, for a description of how the interactive fitting is meant to work and what an appropriate response should be.

Thank you! That is much clearer now.