SN 2022acko and the Properties of Its Red Supergiant Progenitor: Direct Detection, Light Curves, and Nebular Spectroscopy

Abstract We present ultraviolet, optical, and infrared observations of the Type II-P supernova SN 2022acko in NGC 1300, located at a distance of 19.0 ± 2.9 Mpc. Our dataset spans 1–350 day postexplosion in photometry, complemented by late-time optical spectroscopy covering 200–600 days, and includes deep preexplosion imaging. We use this extensive multiwavelength dataset for both direct and indirect constraints on the progenitor system. Using the early time photometry and shock cooling models, we infer that SN 2022acko likely originated from a red supergiant with a radius of R ∼ 580 R ⊙ and an initial mass of M ∼ 9–10 M ⊙ . From the radioactive decay tail, we infer a synthesized 56 Ni mass of 0.014 ± 0.004 M ⊙ . We further model nebular-phase spectra using radiative transfer models and nucleosynthesis yields for core-collapse supernovae, which suggest a progenitor initial mass in the range of 10–15 M ⊙ . Meanwhile, a blackbody fitting of the detected preexplosion counterpart in the F814W and F160W bands indicates a red supergiant with a lower initial mass of approximately 7.5 M ⊙ . The light curve exhibits a 116 day plateau, indicative of a massive hydrogen-rich envelope, inconsistent with the preexplosion analysis. We investigated the discrepancy between direct and indirect progenitor mass estimates, focusing on the roles of binary interaction, early time modeling limitations, and systematic uncertainties in spectral calibration. Our results indicate that there may be tension among mass estimates, potentially arising from modeling limitations and flux calibration uncertainties rather than from insufficient data and highlighting the need for more physically realistic models and a deeper understanding of systematic effects.