Recurrent Symbiotic Nova T Coronae Borealis Before Outburst

TL;DR

This study presents extensive multi-wavelength observations of T CrB from 2011 to 2023, analyzing its variability, accretion processes, and predicting an upcoming outburst in January 2024 based on light curve comparisons.

Contribution

It provides new ephemeris data, analyzes flux ratio variations, detects rapid line variability, and models the binary system parameters, predicting the next outburst.

Findings

Hα/Hβ flux ratio varies from 3 to 8, indicating changing flux ratios between X-ray and optical.

Detected ~25 min variability in HeII λ4686 line and B-band amplitude of 0.07 mag.

Predicted the next outburst of T CrB to occur in January 2024.

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 $JD_{min} = 2455828.9 + 227.55 \times E$ 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 HeII $\lambda 4686$ line with a characteristic time-scale of $\sim 25$ min, the amplitude of variability in the $B$-band was $\sim 0.07^m$. 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 $q=M_{cool}/M_{hot} \in [0.5, 0.77]$, 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.