HighSpec: A High-Resolution Spectrograph for the MAST Telescope Array

We present the updated design of HighSpec, a high-resolution R similar to 20, 000 spectrograph designed for the Multi Aperture Spectroscopic Telescope (MAST). HighSpec offers three observing modes centered at the Ca II H&K, Mgb triplet, and Ha lines. Each mode is supported by a highly optimized ion-etched grating, contributing to an instrument exceptional peak efficiency of greater than or similar to 85% for the two latter bands (greater than or similar to 55% for the Ca II H&K band). Optimizing throughput over wavelength coverage (Delta lambda = 10-17 nm), HighSpec enables the precise measurement of spectral lines from faint targets. This approach is especially relevant for stellar object studies, specifically of WDs, which are intrinsically faint and have few spectroscopic lines. Each observing mode was tailored to target spectral features essential for WD research. Its integration with MAST, an array of 20 custom-designed telescopes that can function as a single large telescope (equivalent to a 2.7m telescope in collecting area) or multiplexing over the entire sky, provides unique adaptability for extensive and effective spectroscopic campaigns. Currently in its final assembly and testing stages, HighSpec's on-sky commissioning is scheduled for 2025.