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3. Next, choose the statistic to use for combining the spectra. There are several options available; the default (Robust Weighted Mean) tends to provide the best results for more than 4 spectra of reasonable S/N.
4. Finally, enter an a base output file name (e.g., "CombSpec_141140-143" - no need to add the ".fits" at the end) and click on "Write File". You . A fire_xvspec viewer window will pop up to display the spectrum (below). You will need to remember that filename for the final telluric correction step. 