The 1987 outburst of the recurrent nova U Sco

Abstract
Optical and infrared observations of U Sco during its 1987 outburst are presented. The interval since the last outburst (8yr) is exceptionally short and places constraints on the thermonuclear runaway model. Spectra early in the decline show broad (FWZI∼10 000 km s−1) near-flat topped lines. On the model of Webbink et al. this would be interpreted as ejection of an optically thin shell. On this model the later data suggest the presence of a brightened disc in the system. The possibility that the disc seen in quiescence is heated by the ejecta is discussed. Similarities between U Sco and the nitrogen flaring stage in classical novae are mentioned. The emission line ratio N III4634/4640+4641 Å is unusually large during the early development of the U Sco outburst.

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