Echelle spectroscopy is a powerful method to provide wide coverage of wavelengths yet to achieve high spectral resolution. The echelle section of IRCS covers the entire , , or band with only one or two grating configurations while achieving the velocity resolutions of 15 - 60 km s. Data reduction of echelle spectra is complicated. In addition to the difficulties in handling spectra of points sources in general, one must take into account the effects like the one that each slit image has a curvature along its length in reducing spectra of extended sources. Cross-dispersed echelle spectra taken with a cross-disperser have curvatures along the direction of the wavelength as well. These curvatures (distortions or tilts) should be corrected.
This document describes handling the echelle data for extended objects obtained with IRCS. The characteristics of echelle spectrosopy and IRCS are introduced for deepening users' understanding about the echelle data.1 This document also must be a good guide for handling spectroscopic data of point sources because the reduction processes for the spectroscopic data of extended sources described here include dealings with spectroscopic data of point sources.2