t₀ = 60083 MJD is taken to be the explosion date of SN 2023ixf.

J, H,  K band magnitudes were measured using the NIR spectra.

CO models were fit adopting a flat continuum (the elevated “pseudo-continuum”) at 2.0–2.3 μm for Model A and a modified black body continuum with carbon dust for Model B.

This spectrum did not cover enough of the CO band emission to allow errors to be estimated.

The errors provided are statistical. In addition to the standard statistical errors provided in the CO mass and temperature columns, the 10–20% uncertainty in the flux value and the telluric correction may result in uncertainties of 100–200 K in temperatures in the fitting process. The CO mass ranges (in parentheses) are estimated, accounting for the error in T_CO of 200 K.

This spectrum was obtained using the K3000 filter (which does not cover the full CO feature) and may be subject to systematic errors due to the novel setup. Additionally, errors in the dust mass could not be estimated.

Statistical errors of the dust temperatures and mass are ∼35 K and ∼0.15 × 10⁻⁵ M_⊙, respectively. The systematic errors in the temperatures are ∼100 K which results in the uncertainties of the dust mass ∼0.8 × 10⁻⁵ M_⊙ (a factor of ∼3 and ∼5 higher, respectively), due to uncertainties in defining the continuum.

The uncertainties in the model fitting include statistical and systematic errors resulting from different choices of the continuum levels.

The values in parentheses are from Rho et al. (2018a) for comparison.