Large-amplitude photometric variations of Nereid

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Nereid, one of the two known satellites of Neptune, was discovered in 1949 by Kuiper1. It has an extremely eccentric orbit (e ≃ 0.75), such that its distance from Neptune varies from ∼1.4 to 9.7 million km, with a period of ∼360 days. No photometric data exist for Nereid2 other than the rough estimate of photographic magnitude (mp Combining double low line 19.5) determined by Kuiper1. In June 1987 we collected photometric (UBVRI) and astrometric data on Nereid using the 0.9-m telescope and CCD camera at the Cerro Tololo Inter-American Observatory (CTIO). We obtained four astrometric positions and UBVRI reflectances spanning 8 days. From these data, an unusual reflectance spectrum for Nereid was determined. Variability of Nereid was observed in all bandpasses, with an amplitude of greater than 1.5 mag, and a probable period of between 8 and 24 h. © 1988 Nature Publishing Group.

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