The mid-infrared spectral development of Nova Cen 1986

Abstract

We have monitored the mid-infrared spectrum (8–13 μm) of Nova Cen 1986 for a 2.5-yr period, from day 146 until 883 d after outburst, when it became too faint to observe further. During that period the infrared spectrum showed evidence for emission from three separate dust components: (i) warm carbon-based grains, as commonly found in dust-forming novae; (ii) silicate grains; and (iii) small grains or large molecules such as polycyclic aromatic hydrocarbon (PAH) or hydrogenated amorphous carbon (HAC). The presence of both carbon and silicate grains in the ejecta implies a substantial chemical and/or spatial non-uniformity within the ejecta. Nova Cen 1986 is the first nova in which the unidentified infrared (UIR) features (and hence PAHs or HACs) have been observed. In the nova ejecta, where carbon grains are amorphous, the HACs are the more likely source of the UIR features.