Constraints on the Progenitor of SN 2023bee from its Nebular-Phase Spectra

Abstract: We present late-time photometry (~100-400 days after peak) and nebular-phase optical/NIR spectroscopy (100-360 days) of the Type Ia supernova (SN Ia) SN 2023bee. This SN Ia was observed TESS immediately before and after explosion and showed a relatively weak early excess light-curve feature detected in multiple UV and optical bands. Possible explanations for this early excess feature include interaction between the SN ejecta and a non-degenerate companion, or the decay of radioactive isotopes synthesized near the ejecta surface in a sub-$\text{M}<em>\text{Ch}$ double-detonation scenario. However, the degeneracies and incompleteness of existing models have so far prevented a definitive conclusion about its progenitor system. Nebular-phase spectra provide a complementary probe of SN Ia progenitors by constraining stripped H/He-rich material and iron-group abundances sensitive to the progenitor white dwarf density. We report the non-detection of narrow H/He features in nebular phase optical/NIR spectra of SN 2023bee, placing upper limits of $$m^{{\text{stripped}}}</em>\text{H}\lesssim5.0\times10^{-3}\text{ M}<em>\odot$$ and $$m</em>\text{He}^{{\text{stripped}}\lesssim1.2\times10^{-4}\text{} M}<em>\odot$$. These limits strongly disfavor a non-degenerate companion and suggest that companion interaction is unlikely to explain the early excess of SN 2023bee. We also performed line-diagnostic measurements on the 7200 Åcomplex using multi-Gaussian fitting and continuum estimation, with the inferred velocities validated against NIR spectrum at the similar phase. The resulting low Ni-to-Fe mass ratio, $m</em>\text{Ni}/m_\text{Fe}\lesssim 0.06$, is broadly consistent with a sub-$M_{\text{Ch}}$ double-detonation progenitor system.