The evolution of photospheric temperature in nova V2676 Oph toward the formation of C2 and CN during its near-maximum phase

The molecular formation of C2 and CN in the dust-forming classical nova V2676 Oph occurs during its near-maximum phase. We investigated the temporal evolution of the photospheric temperature of the nova as it approached molecular formation during its early phase. The effective temperature of the nova around the maximum decreased from ∼7000 K to ∼5000 K over the course of ∼3 d. The molecules formed at temperatures of <∼5000 K. Such low temperatures of nova photosphere and low expansion velocities along with carbon-rich atmosphere might play an important role in achieving conditions favorable to the molecular formation of C2 and CN in V2676 Oph.