Evolution of the optical emission lines and the X-ray emission during the super-active stage of T CrB

Abstract

T CrB is a symbiotic star that experiences nova outbursts every ∼ 80 yr. The next, long-anticipated nova outburst should occur during the 2024--2026 period. Here, we present results of high-resolution optical spectroscopy of T~CrB in the period 2016--2023. In these spectra, we measured the equivalent widths of the Hα, Hβ, HeI and HeII emission lines. The maximum equivalent width (EW) was recorded on May 2021, when the EW of Hα reached -44.6Å and Hβ = -21.5 Å. At the other extreme, the minimum of EW(Hα) = -2.9 Å was recorded in October 2023. After October 2023, the B-band emission brightened, suggesting a re-appearance of the orbital modulation. In addition to the optical data, we study the X-ray behaviour in the same period. We find a strong correlation between EW(Hα) and X-ray flux with a correlation coefficient -0.78 and a significance of 2.6×10^{-5}.