The peculiar infrared temporal development of Nova vulpeculae 1987 (QV Vulpeculae)

We report 1.25-19.5 μm infrared photometry and optical/infrared spectroscopy of Nova QV Vul (1987) from 1987 November through 1989 September. The measurements show that an optically thick carbon dust shell formed within 83 days of the outburst, and that the spectral signatures of four types of astrophysical grains appeared at various times during a 2 year period following the eruption. Carbon, SiC, and hydrocarbons formed first; oxygen-rich silicates formed later. The ejecta in which the optically thick carbon grain shell condensed were apparently moving at nearly 3 times the velocity of the principle ejecta responsible for the early emission from the hot gas pseudophotosphere. We suggest the possibility that the carbon dust components formed in fast-moving polar plumes, and that the silicates formed in a slow-moving equatorial ring. Mass estimates from the infrared photometry and optical spectroscopy confirm that grain condensation in both the slow and fast ejecta of QV Vul is consistent with constraints established by previous observations of other dusty novae. The physical properties of the dust condensation zones are discussed, and numerical estimates of the dust mass are given for carbon and silicates. We conclude that the condensible elements in these grains were present in approximately solar abundance.