2026RNAAS..10...36R

V3661 Ophiuchi has the fastest rate of brightness decline of any Fe II type nova observed to date. Here we present its spectrum (from 0.47 to 2.5 μm) 130 days after visible maximum. The spectrum shows both very low and very high excitation permitted and forbidden emission lines. Modeling of the spectrum indicates that the line features arise in a radiation bounded region illuminated by a extremely hot (T > 6 × 10⁵ K) and luminous ionizing source. In addition to producing V3661 Ophiuchi's numerous coronal lines, illumination by the hot source generates a warm, partially ionized zone at the back of the emission line region that gives rise to its lowest excitation emission features.