Recent UBV photometry of T CrB

ATel #17784; Marchev, D. ; Borisov, B. ; Atanasova-Sartliiska, T. ; Yordanova, G. ; Georgiev, A. (Konstantin Preslavsky University of Shumen); Marchev, V. (Institute of Astronomy and National Astronomical Observatory, Bulgaria)
on 9 May 2026; 14:36 UT
Credential Certification: Vladislav Marchev (vlad.marchev@gmail.com)

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We present our recent photometric observations of T CrB obtained on the 5th and 6th of May 2026 and we compare them with the ones from ATel#17052 an year ago. Observations were conducted with 40 cm MEADE LX200ACF telescope and a CCD camera FLI PL09000 with a filed of view: 31x31 arcmin and resolution: 0.61 arcsec/pixel at the observatory of the Shumen University "Episkop Konstantin Preslavski" (Kjurkchieva et al. 2020) The observations were performed in a 3.1 hour time frame during both nights with 60 exposures for both filters U, B and V and respective exposure time 120s, 20s and 5s.. The average values with the respective uncertainty for the first night are as follows: in U=11.852+/-0.018, B=11.610+/-0.010 and V=10.253+/-0.007. The values obtained during the second night are very similar. The data shows that brightness of the star has returned to the state it was back in 2015. Comparing the values published by Yankova et al. (2026) which were obtained at 2024 we see the brightness has declined in U with 1 magnitude and in B and V filters with around 0.5 magnitude. In our most recent observations, we see 0.350 magnitudes of flickering in U filter while in 2025 it was observed around 0.417 magnitude as for B we see an increase from 0.07 in 2025 to 0.15 magnitude of flickering now and for V it was 0.10 in 2025 and now it is 0.05. It is expected for recurrent novae like T CrB to have a significant decrease in brightness and have a generally lower state before eruption. If the current trend for decreasing brightness continues we can probably expect the nova eruption to happen in the next 5-6 months based on calculations for the mass accretion rate and the critical mass needed to start the process conducted in the PhD thesis of Vladislav Marchev (2025). The light curve from 05.05.2026 is presented in the figure below. This study was performed with the help and funding from Ministry of Education and Science of Bulgaria (Bulgarian National Roadmap for Research Infrastructure) RACIO and Scientific Research Found of Shumen University.

T CrB light curve from 05.05.2026