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 $JD_{\textrm{min}}=2455828.9+227.55E$ 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 ${∼}0\overset{\textrm{m}}{.}07$. 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 $q=M_{\textrm{cool}}/M_{\textrm{hot}}\in[0.5,0.77]$, the orbital inclination $i\in[55^{\circ},63^{\circ}]$. 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.