T CrB: the active spectroscopic state (2014-2023) is over

ATel #16109; F. Teyssier, J. D. Hinnefeld, C. Boussin, I. Diabassoura , J. Guarro Flo, F. Sims, A. Leduc, S. Curry, D. Boyd, D. Cujedo (ARAS Group), S. N. Shore (Univ. of Pisa)
on 30 Jun 2023; 18:29 UT
Distributed as an Instant Email Notice Novae
Credential Certification: S. N. Shore (shore@df.unipi.it)

Tweet

The symbiotic recurrent nova (1866,1946) T CrB experienced a new active phase active phase since 2015 (Ilkiewicz & al., 2016, Munari & al., 2016) peaking in April 2016. The ARAS Eruptive Stars Group has regularly observed the evolution of the system with more than 750 spectra secured since 2013 with a variety of small telescopes and spectrographs ranging in resolution from 600 to 15000 (grism, grating, and echelle; observers and instruments are listed on the ARAS URL). After the peak of activity (2016 Apr) characterized by an increase in the blue continuum and the nebular radiation, in the intensity of the Balmer lines, the appearance and strengthening of higher ionization lines (He I, He II), the system began a slow decline until 2020 followed by a plateau in 2021-2022, although with an upturn in 2022. At the beginning of 2023, the equivalent widths of the emission lines were about the same as those observed during previous orbital cycles at the same phase (Lines & al, 1988). The high cadence monitoring allowed us to detect a stepped decrease of the intensities by a factor 2 in April between JD 2460043 - 2460050. He II 4686 became almost indistinguishable except by comparison with the spectrum of a normal red giant of type M4III, following the method described by e.g. Mikolajewska & al., 1989. Since then, the emission line intensities have remained at this low level and continued to decline at the level observed in 2013-2014, before the onset of the active state. Our last flux calibrated spectrum obtained on June, 29 (JD 2460124.70) gives F(H alpha) = 3.1 E-12, F(H beta) = 3.1 E-13 and F(He II) < 5 E-14 in units of erg cm^-2 s^-1 to be compared to the values (1.1 - 6.8) E-12, (1.8 - 17.0) E-13 and (3 - 48) E-14 in 2013-2014 before the active phase (Ilkiewicz & al., 2016). We conclude that the active state 2015-2023 is over. The ARAS observers are continuing this monitoring. Spectra are openly available at the URL listed below and graphs and further information is available at Graphs and monitoring: http://www.astronomie-amateur.fr/EruptiveStars/TCrB0.html Table of equivalent widths (A): Mean (Min - Max) \begin{table}[!ht] \centering \begin{tabular}{|l|l|l|l|l|} \hline \# & Epoch & H alpha & H beta & He II 4686 \\ \hline 1 & 2013-2014 & 6.9 (2.2-13.0) & 4.0 (1.9-6.3) & 0.8 (0.1-2.7) \\ \hline 2 & 2016 & 41.9 (32.7-54.2) & 22.7 (17.6-31.1) & 12.0 (6.5-18.5) \\ \hline 3 & 2023 01-04 & 24.9 (16.9-29.5) & 14.8 (12.3-15.5) & 3.3 (2.6-4.6) \\ \hline 4 & 2023 04-06 & 13.4 (7-18.1) & 7.0 (4.1-10.6) & 1.1 (0.3-1.9) \\ \hline \end{tabular} \end{table}

ARAS spectral datase