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

TL;DR

This study tracks the evolution of optical emission lines and X-ray emission in T CrB from 2016 to 2023, revealing a strong correlation and preparing for its upcoming nova outburst around 2024-2026.

Contribution

It provides the first detailed high-resolution spectroscopic and X-ray analysis of T CrB during its super-active stage leading up to a predicted nova outburst.

Findings

Maximum EW of Hα reached -44.6 Å in May 2021

Strong correlation between Hα EW and X-ray flux (-0.78)

Optical brightening suggests re-appearance of orbital modulation

Abstract

T CrB is a symbiotic star that experiences nova outbursts every $\sim$ 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 H$\alpha$, H$\beta$, HeI and HeII emission lines. The maximum equivalent width (EW) was recorded on May 2021, when the EW of $H\alpha$ reached -44.6 \AA and H$\beta$ = -21.5 \AA. At the other extreme, the minimum of EW($H\alpha$)= -2.9 \AA 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 $EW(H\alpha)$ and X-ray flux with a correlation coefficient -0.78 and a significance of 2.6$\times 10^{-5}$.