2017ApJ...840....1M

We present the first identification of a candidate precursor for an imminent red nova. Our prediction is based on the example of the precursor to the red nova V1309 Sco, which was retrospectively found to be a contact binary with an exponentially decreasing period. We explore the use of this distinctive timing signature to identify precursors, developing the observational and analysis steps needed. We estimate that our Galaxy has roughly 1-10 observable precursors. Specifically, we lay out the observational case for KIC 9832227, which we identified as a tentative candidate two years ago (Molnar et al. 2015, AAS Meeting #225 Abstracts 415.05). Orbital timing over the past two years has followed the tentative exponential fit. As of late 2015, the period time derivative went beyond the range found in other systems ({dot}P | 1×10^–8| ), a necessary criterion for a serious candidate. We estimate time of merger is the year 2022.2 ± 0.7. Double absorption line spectra confirm directly the 0.458-day light-curve is the orbital period of a contact binary system and yield a mass ratio m_B/m_A=0.228±0.003. Closer analysis of the Kepler timing data shows evidence of a component C with orbital period P_C=590±8 days and m_Csini_C=0.11 M_☉. An alternative interpretation of the long-term timing trend, that is, a light travel-time delay due to the orbit around a distant component D, is ruled out by the spectroscopic data for any nondegenerate star. Additional measurements are needed to test further the merging hypothesis and to use fully this fortuitous opportunity.