Determination of the dispersion solution: the IDENTIFY task

The IDENTIFY task is used to identify comparison lines in a one-dimensional spectral image and to determine the dispersion solution. The comparison lines must be taken ideally in the same configuration with object frames. The comparison lines can be usually obtained from the calibration lamp emitting Th-Ar lines. In the near infrared $J$-, $H$-, and $K$- bands, there are many OH sky emission-lines and telluric absorption lines (Maihara et al., 1993; Rousselot et al., 2000; Oliva & Origlia, 1992). These lines can be obtained from sky frames taken at positions near the objects or from object frames themselves under the same instrument configurations as those for the object frames. The OH sky emission lines thus offer the best conditions to obtain accurate dispersion solution.