Predictions for Upcoming Recurrent Novae Eruptions; T CrB in 2023.6±1.0, U Sco in 2020.0±0.7, RS Oph in 2021±6, and more

The prediction of upcoming recurrent nova eruptions has good utility for promoting a frequent watch so that the usually-very-short eruptions are not missed and caught early, plus allowing for the pre-organization of intense observing campaigns. Such efforts are highlighted by my prediction of the 2010 eruption of U Sco, where spacecraft targets-of-opportunity programs were in place in advance and workers watched the target several times a day for over a year, then resulting in measured magnitudes averaging every three minutes for the entire eruption, plus daily and hourly spectra and UBVRIJHK photometry, plus X-ray, gamma-ray, far-IR, IR, and UV spacecraft observations, leading to the all-time best observed nova eruption and the discovery of two new phenomena. Recurrent novae are a particularly important subset of all novae, and they have the advantage that their eruptions can be predicted with useable accuracy. Inter-eruption times can be predicted from the brightness during quiescence, and by looking at the history of inter-eruption intervals. For T CrB, with eruptions in 1866 and 1946, a simple constancy of interval suggests the next eruption will be in 2026. But a better prediction is based on the pre-eruption-plateau with a rise to the plateau from 1936.0-1939.6 before the fast 1946.1 eruption, so with T CrB showing the same rise from 2014.2-2016.4 up to the current plateau, the next eruption will be in 2023.6±1.0. For the long history of intervals for U Sco (averaging 10.6 years), the next eruption should come in 2020.7±1.6. But U Sco was substantially bright in 2011-2012, with higher accretion, so it should accumulate the trigger mass substantially before 2020.7. Given that it has not erupted as of this writing, I predict a date of 2020.0±0.7. For RS Oph, based on its rather variable intervals, the next eruption should start in 2021±6. V394 CrA, CI Aql, V3890 Sgr, and V2487 Oph should go off any year now, but there is no high confidence for setting a date.