High-Resolution spectroscopy

IGRINS-2 is operated in a single, high-resolution spectroscopic mode. This mode provides full wavelength coverage between 1.49-1.80 μm (H-band) and between 1.96-2.46 μm (K-band) region at a spectral resolution of R~45,000. These two spectroscopic channels, composed of two separate detectors (H- and K-bands), are being obtained simultaneously.

Optical layout

The input optics reimages the telescope pupil into a cold stop before refocusing it on to the slit plane. The light reflected by the slit mirror is then directed to the slit viewing camera, while the light passing through the slit is collimated by an off-axis mirror before reaching the immersion grating. The dispersed beam is then collimated and directed to a high efficiency dichroic, which splits the light between the H and K arms of the spectrograph. Once again, each H and K beams are collimated before being cross-dispersed and finally enter the refracting cameras and reach the detectors.

Spectral range and resolution

IGRINS-2 makes use of a silicon immersion grating as the main disperser and two VPH gratings as cross-dispersers. The resulting resolving power is R~45,000.

The coverages of the different orders in which the light is dispersed are provided below.

Sensitivity

The final evaluation of the instrument performance is in the process of being completed. However, the following table provides preliminary estimates for the signal-to-noise ratio for 3,600s (6x600s) integration on a point source in the 70%-ile image quality, 50%-ile cloud cover (clear).