Resolve discrepancies in the atmospheric ionization and spectral formation models
Determine whether the inability of the spherically symmetric NLTE expanding-atmosphere models to reproduce all observed optical features results from an incomplete C II–III–IV ionization structure, wind asymmetry caused by surface rotation, scattering by surrounding dusty material, or an alternative identification of the weak feature near 5800 Å.
References
Some discrepancies in the line intensities, as well as the difficulty in reproducing the feature near $\lambda 5800$, could not be solved despite our efforts. For example, we have included X-rays, which are expected from shocks arising from instabilities within a stellar wind. However, it had virtually no impact on the optical spectrum. The inability to simultaneously reproduce all observed features may indicate that the atmospheric ionization structure (e.g., the \ion{C}{ii-iii-iv} balance) is not fully captured by our models. This could arise, for example, if the emerging wind of SO is not symmetric, as assumed here. Surface rotation, for example, could break the spherical symmetry and produce latitudinal-dependent wind properties. Furthermore, the central star is not detected in direct imaging, and its optical spectrum may be observed through scattering by the surrounding dusty material, as suggested for V605 Aql \citep[][]{clayton2006}. We cannot rule out that scattering modifies the observed [WR] spectrum. The weak feature near $\lambda 5800$ may also have an identification other than \ion{C}{iv}. Future observations will be essential to clarify these issues, particularly as the central star continues to reheat and \ion{C}{iv} transitions may become prominent.