Recurrent Symbiotic Nova T Coronae Borealis before Outburst

Abstract

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\(\alpha\)/H\(\beta\) varied from \({\sim}3\) to \({\sim}8\) 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\(\alpha\)/H\(\beta\) 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 \(\lambda 4686\) line with a characteristic time-scale of \({\sim}25\) min, the amplitude of variability in the \(B\)-band was \({\sim}0\overset{\textrm{m}}{.}07\). 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 \(\mu=1.0\), 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.