A sudden increase of the accretion rate in T Coronae Borialis

ATel #17030; Veronika Schaffenroth, Eike Guenther, Hans-Peter Doerr, Birger Aufschlaeger (Thueringer Landessternwarte Tautenburg)
on 11 Feb 2025; 15:34 UT
Credential Certification: Veronika Schaffenroth (schaffenroth@tls-tautenburg.de)

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We report a recent sharp increase in the height of the emission lines seen in the spectrum of the recurrent nova T CrB. We are monitoring this system more or less regularly with the Echelle spectrograph mounted in the Coude focus of our 2m-Alfred Jensch telescope in Tautenburg for about a year. We are using a wavelength coverage of 4590 to 7350 angstroms and a resolution of R=65000. This wavelength region covers the Halpha and Hbeta Balmer lines, as well as several He I and He II lines, which are shown in emission and are resulting from the accretion disk around the massive white dwarf. During the last about 2.5 weeks, we measured a constant increase in the height of the hydrogen emission lines. The equivalent width of the hydrogen lines doubled from 21.01.2025 to 09.02.2025. The line profile also underwent significant changes from a double-peaked shape with a central absorption to a single emission peak. Similarly to what was observed in Atel #16912, the He emission lines also start to reappear, which vanished again in December last year. The equivalent width of the helium lines has increased by a factor of more than four since 21.01.2025. This is seen in He I 5875,6678 and 7065 as well as in the He II 47686 line. In the He I 5876 line, a second red-shifted peak at 5876 angstroms appeared in addition to the blue-shifted peak at 5874, which was already visible before. The short appearance of the He emission lines in the spectrum of T CrB in November last year coincided with a spike in the light curve of T CrB. However, presently, no increase in the light curve has been observed so far. The current spectral changes indicate a strong increase in the accretion rate, which will eventually result in a Nova eruption, as predicted to occur this or next year (e.g., Schaefer et al. 2023). We will continue to monitor this source. Plots of the spectral changes can be found in the cited website.

Observing campaign on T CrB at the Thueringer Landessternwarte Tautenburg