U Leonis

In the Bonner Durchmusterung catalogue BD +14°2239 was listed as magnitude 9.5. No star at that position and anywhere near that bright has been seen since, suggesting that perhaps it was a nova which has since faded. It has been given the designation U Leo. A nearby 17th magnitude star shows sinusoidal variations of about 0.11 magnitudes with a period of 3.204 hours. That behaviour is quite consistent with it being an old nova. However, the spectrum is that of a F-type main sequence star and there is no evidence of either a white dwarf companion or an accretion disc.

In 2019 the British Astronomical Association Variable Star Section mounted a campaign to observe this strange object. On the nights of 2020-01-04, -21 and -24 I took almost a thousand 30-second unfiltered exposures of U Leo. The data has not yet (2020-04-26) been fully analyzed but a preliminary light curve does appear to show variability with the expected magnitude and period.