Recurrent Symbiotic Nova T Coronae Borealis before Outburst

The results of photometric and spectral observations of T CrB obtained in a wide range of wavelengths in 2011–2023 are presented. We use the near-IR light curves to determine a new ephemeris JD_min=2455828.9+227.55E for the times of light minima when the red giant is located between the observer and the hot component. The flux ratio H α /H β varied from ∼3 to ∼8 in 2020–2023, which may be due to a change in the flux ratio between the X-ray and optical ranges. It is shown that the value of H α /H β anticorrelates with the rate of accretion onto the hot component of the system. Based on high-speed follow-up observations obtained on June 8, 2023, we detected a variability of the He II λ 4686 line with a characteristic time-scale of ∼25 min, the amplitude of variability in the B -band was ∼0m.07 . Simulations of the near-IR light curves accounting for the ellipsoidal effect allowed us to obtain the parameters of the binary system: the Roche lobe filling factor of the cool component μ=1.0 , the mass ratio q=M_cool/M_hot∈[0.5,0.77] , the orbital inclination i∈[55^∘,63^∘] . A comparison of the light curve obtained in 2005–2023 with the 1946 outburst template made it possible to predict the date of the upcoming outburst—January 2024.