T CrB didn’t erupted “before September 2024”,
as naively prophesied and widely reported in the press and popular science magazines since March.
Analysis of the photometric curves B, V, Vis. can give nothing more than a very qualitative approximation of the rate of accretion of matter (H and He) to the surface of the white dwarf,
and in no way provide a prediction of the timing of the outburst nova: between 2015 and 2024-04, the increase in luminosity B, V shows that the accretion rate has increased.
More precise estimates of the accretion rate have been proposed based on the study of X-rays.
The expected nova outburst will occur when the accreted mass is sufficient for the critical pressure to be reached at the base of the envelope,
and the temperature to be sufficient to trigger the cold then hot CNO cycles.
Estimates of the accretion rate are fraught with uncertainty AND we don't have the full history of T CrB since the 1946 outburst (regular monitoring has only been available since the early 1990s).
It is therefore impossible to predict the timing of the next outburst (There is only one known recurrent nova, which explodes with an astonishing regularity of around 1 year. It is located in the Andromeda galaxy).
From the recurrence time observed between the 1866 and 1946 outbursts, we can say that we are in the range where the outburst may occur: tonight, in a few months, or in a few years.
We have been monitoring T CrB on a regular basis since 2012, collecting almost 1,500 spectra and no less than 580 in 2024 alone.
It is thanks to this regular monitoring that we have been able to identify a significant increase in the degree of ionization of the system,
with the appearance of He I, He II and NIII emission lines, with the spectra obtained by Forrest Sims and confirmed by an echelle spectrum obtained by Joan Guarro,
in the context of an overall increase in the flux of HI lines (see, for example, the latest spectrum secured by Etienne Bertrand).
This increase in system activity follows very low activity in 2024, after the end of the very state.
It is too early to know what this new active phase corresponds to. It could be a short flare, an active state like those observed in the ‘90s, a big active phase such as 2015-2024 or something new.
What is sure is that the accretion rate has increased in comparison to 2024, thus increasing the mass of the envelope more quickly.
The community is informed by an ATel with the the invaluable support of Steve Shore.
https://www.astronomerstelegram.org/?read=16912
The table in a presentable form:
In units of erg/s/cm^2
Date JD He II He I 5876 H beta He II / H beta He II / He I
632.5 7.20E-13 1.19E-12 3.26E-12 0.22 0.61
2024-11-16.039 630.5 6.70E-13 1.05E-12 2.92E-12 0.23 0.64
2024-11-15.041 629.5 7.63E-13 1.15E-12 3.05E-12 0.25 0.66
2024-11-14.044 628.5 5.8E-13 1.06E-12 3.26E-12 0.18 0.55
2024-11-13.041 627.5 1.46E-12 1.08E-12 3.84E-12 0.38 1.35
2024-11-12.041 626.5 9.412E-13 1.06E-12 3.523E-12 0.27 0.89
2024-11-11.043 625.5 9.101E-13 1.118E-12 3.625E-12 0.25 0.81
2024-11-10.043 624.5 1.53E-12 1.142E-12 4.353E-12 0.35 1.34
2024-11-08.045 622.5 5.568E-13 5.72E-13 2.779E-12 0.20 0.97
2024-11-05.048 619.5 2.622E-13 5.43E-13 2.041E-12 0.13 0.48
But the story is not over..
The study of T CrB during the next weeks will make it possible to determine the nature of the active phase that we have just detected.
The only problem is the very low height of our target, less than 30 degrees for most of observatories.
Observers who contribute to the base are asked to do their best to obtain spectra during these few difficult weeks before T CrB returns to the morning sky.
but also to those who have not yet participated, and who have Nordic observatories to try to obtain T CrB spectra, even if the SNR is low and atmospheric correction is made more difficult.
Due to the interest of this new phase, spectra obtained with SA100 or 200 are very welcome, even if they do not meet the criteria required for the ARAS ES database (R > 500)
Spectra to be sent to
francoismathieu.teyssier@gmail.com and copy to
arasdatabase@gmail.com
Many thanks to the contributors and to Steve
