Presence of He II 4686 Å on day 5.73

Determine whether He II 4686 Å emission is present in the day 5.73 optical spectrum of V1674 Herculis by deblending it from the overlapping N III 4638 Å feature.

Background

At early times, the spectral region near 4686 Å is dominated by a broad N III 4638 Å emission complex, complicating identification of any nascent He II 4686 Å emission. Clear He II 4686 Å appears later (from day 19.87) as ionisation increases.

Resolving whether He II 4686 Å is already present on day 5.73 would clarify the timeline of ionisation changes in the ejecta.

References

On day 5.73, He II 4686 Å seems to be present on the right edge of the feature centred at 4637 Å. However, the broad N III 4638 Å line makes it difficult to confirm the presence of the He II 4686 Å line (see Figure \ref{fig:He_II}).

— Optical observations of the fast nova V1674 Herculis  (2602.19940 - Rawat et al., 23 Feb 2026) in Spectral Evolution — Early Spectra: day 1 to 6