2025ApJS..281...28M

We present the first data release of the Hawaii Infrared Supernova Study (HISS), consisting of a large sample of near-infrared (NIR) spectra, 0.7-2.5 μm, obtained with the Keck-II/NIRES and IRTF/SpeX spectrographs. This sample is comprised of 90 NIR spectra of 48 transients, spanning from hours after explosion to ≥+350 days. Acquired over 3 yr (2021-2024), this data release includes 17 Type Ia supernovae (SNe), 15 Type II SNe, eight stripped envelope SNe, six interacting SNe, one tidal disruption event, and one SLSN-I. These spectra were all systematically reduced using either the Python-based reduction code PYPEIT or the IDL-based SPEXTOOL and constitute one of the largest NIR samples of transients available to the astrophysical community. We show the utility of NIR spectra and identify the key spectral features across multiple types of SNe. We demonstrate how both early-time and nebular-phase NIR spectra of SNe can be used to investigate the physics of the explosion, and to reveal the properties of the progenitor. With the addition of this data set, the number of publicly available NIR spectra spanning multiple transient types has been substantially increased. In its next phase, HISS will leverage target-of-opportunity spectral observations and NIR imaging from telescopes on Maunakea. Expanding the NIR data set of SNe is vital to the transient community, particularly in light of the increasing emphasis on the infrared regime following the recent launch of the James Webb Space Telescope and the forthcoming launch of the Nancy Grace Roman Space Telescope.