Formation of C2 and CN in nova V2676 Oph around its visual brightness maximum.

The slow nova V2676 Oph was unique in that both C2 and CN molecules were observed during its early phase around the visual brightness maximum. The absorption bands of these molecules were detected using spectroscopic techniques and disappeared within several days. The formation of CO was followed by dust formation, which was confirmed via observations in the latter phase of the nova. The formation of molecules is critically important in understanding the origin of dust grains in novae; however, the formation mechanism of C2 and CN molecules in the early phase of novae remain unclear. Here we report optical spectroscopic observations of the dust-forming nova V2676 Oph in the early phase, and we use these data in addition to spectroscopic observations reported previously to discuss the origin of diatomic molecules in the nova. We conclude that C2 and CN molecules formed in the nova outflow when the outer gas envelope cooled sufficiently and that they survived for more than 2 days but less than 7 days in the nova outflow. [ABSTRACT FROM AUTHOR]