Program: GS-2022A-Q-120

We propose to conduct ToO spectroscopic follow-up observations of infant (i.e. a few hours to a few days post-explosion) supernovae (SNe) and rapidly-evolving transients discovered by the KMTNet Supernova Program (KSP). Observations during early phases can provide crucial insights into both their explosion mechanisms and progenitor systems, with detailed behavior depending on the progenitor radius, envelope structure, composition, mixing of radioactive elements, non-spherical behaviour, as well as interactions with circumstellar material (CSM) and/or binary companions. KSP is uniquely capable of probing these processes by providing continuous, high-cadence, multi-band optical light curves, and has been shown to be capable of triggering prompt spectroscopy within ~1 day after first detection. Follow-up spectroscopic observations of the infant phase can critically enhance our understanding of how SNe explode and the enigmatic nature of rapidly- evolving transients. We request ToO triggers in order to obtain prompt GMOS-S spectroscopy of ~3 infant SNe and peculiar transients up to 6 magnitudes below their peak luminosity. These spectra will allow us to measure redshifts, ejecta velocities, SN/transient types, abundances, and the presence of CSM, all of which provide vital constraints for modeling their origins and evolution.