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RS Ophiuchi is a recurrent nova consisting of an M2 red giant and a blue companion star. It has undergone five known outbursts, in 1898, 1933, 1958, 1967, and 1985, reaching maximum brightness between 5th and 6th magnitude within a day. It shows significant light variability between outbursts, oscillating between visual magnitudes 9.6 and 13.5. Using the photographic data from Harvard plates from 1890 to 1917 and AAVSO visual data from 1920 to mid-1993, we studied the light behavior of each of the outbursts and searched for periodic brightness variations between outbursts. The shape and the decline rates of the outbursts are strikingly similar to each other. We note here the possibility of an additional unreported outburst in 1945 and support this by the similarity of its decline after 70 days to that of other outbursts. We analyzed the intervals between outbursts using date-compensated discrete Fourier transforms (Ferraz-Mello 1981). We find that while each well observed interval from 1933 to mid-1993 shows strong periodicity within itself, there is no principal period that is common to all and the strongest periods range between 941 and 2283 days.
We gratefully acknowledge the support of NASA under grant NAGW-3228 and the AAVSO Margaret Mayall Assistantship which partially funded this project.
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