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

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-${\text{M}}_{\text{Ch}}$ 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 $m_{\text{H}}^{\text{stripped}}\lesssim 5.0\times {10}^{-3}{\text{ M}}_{\odot }$ and $m_{\text{He}}^{\text{stripped}}\lesssim 1.2\times {10}^{-4}{\text{ M}}_{\odot }$. 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, $m_{\text{Ni}}\mathrm{/}{m}_{\text{Fe}}\lesssim 0.06$, is broadly consistent with a sub-$M_{\text{Ch}}$ double-detonation progenitor system.