SIMBAD references

Nova Cas 2020 was a second example of a classical nova forming both C₂ and CN molecules during its near-maximum phase. The formation C₂ and CN is indicative of the carbon-rich (C/O > 1) gas envelope of the nova. Our low-resolution spectroscopic observations in the optical from UT 2020 July 31 to August 19 revealed the appearance and the disappearance of the molecular absorption bands of C₂ and CN in Nova Cas 2020. These molecules were present during ∼3 days only. Based on analysis of the C₂ Swan band profiles, C₂ (and probably CN also) formed at ∼5000 K in the nova envelope (see ∼8000 K for typical novae at their visual brightness maxima). Spectral evolution and the formation conditions of the molecules are similar to those of V2676 Oph, which is the first example of a C₂/CN-forming nova. We predict that a late-phase grain formation episode similar to that seen in V2676 Oph will occur in Nova Cas 2020.