The Reduction Steps

In the remainder of this document, we’ll use data for NGC 3031 (M81), a nearby galaxy with emission filling the slit to illustrate the reduction. Table 1 shows the particular configuration used for the science target and standard star.

Table 1 Observational setup

Object

Camera

Grating

Prism

Slit

Dither pattern

Science target

SB (0.15”/pix)

32 l/mm

SXD

0.3”

3 x ABBA, q = 0”, 50”a

Standard star

SB (0.15”/pix)

32 l/mm

SXD

0.3”

2 x ABBA, q = 1”, -2”

a Extended galaxies; unguided offset to blank sky.

It would probably be a good idea to initialize your IRAF uparm directory (i.e., remove all the files from it) before starting the process. We will then create an input file list and run XDGNIRS (on your command line, not from within IRAF/PyRAF). We’ll assume that the raw data are in a directory called “example_data,” and we would like to perform the reduction in a directory called “example_reduction.”

cd example_data
ls N*fits > inputfiles.lst
cd ../example_reduction
mv ../example_data/inputfiles.lst .
xdpiped inputfiles.lst  rawdir=../example_data despike_std=yes shift_to_rest=yes

The impatient reader can run the above command and then look at the resulting “NGC3031.fits” or “NGC3031_data_sheet.pdf” files (in the PRODUCTS folder) to see the final result. Alternatively, use the “step” and “stop” options to run one step at a time and follow along with the manual. The available steps can be seen by typing:

xdpiped -h

In v3.0 they are:

0: Identify files and create lists
1: Clean the data with cleanir.py
2: Prepare the data (with nsprepare) and measure some statistics
3: Make the flatfield
4: Reduce the science target and standard star data (de-spike, flatfield, and sky subtract)
5: Rectify and wavelength-calibrate the data
6: Combine the files
7: Extract spectra
8: Remove the H lines in the standard star
9: Perform the telluric line cancellation
10: Flux calibrate the science target spectrum
11: Combine the orders
12: Create an error spectrum
13: Create an informational PDF file

Step-by-step instructions and examples: