T CrB before its new nova event

[Francois Teyssier]

After a short "flare" (less than 10 days) T CrB returns to very activity with H alpha very faint.

H alpha lux from flux calibrated spectra:

http://www.astronomie-amateur.fr/Erupti ... a_2024.png

Link to the page: http://www.astronomie-amateur.fr/Erupti ... TCrB0.html

François Teyssier

[Francois Teyssier]

Faint enhancement of B and V mag
Current orbital cycle in black.
It will be interesting to see how Balmer lines reacts.

TCrB_2024-06-14.PNG (112.17 KiB) Viewed 10637 times

[Joan Guarro Flo]

Hello at all,

T CrB continues showing its secrets, you can see here some aspects of some of its Hydrogen lines and its oxygen line on 5577 Angs.

These graphics were the outcomes of observations with the Piera Remote Observatory equipment.

Best regards, J.Guarro.

[Joan Guarro Flo]

Hello everyone again,

Photometry is a very nice complementary tool to spectroscopy, in this way, I made some tests with different options, equipment, and software.

Nowadays, it seems that the best software for photometry is the AstroImageJ one, the procedure is to use one star as a comparison and one or two more as a check star.

I have been obtaining acceptable results with one old Comet Catcher, 140mm. diameter 500mm. focal length plus a Bessel V filter and an ATIK 460EX camera.

With this equipment, and meanwhile, I was taking spectroscopy to T CrB, I took advantage of taking photometry of this star too. You can see some pictures of it, if you need more information don't hesitate to contact me.

Best regards, J. Guarro.

[Francois Teyssier]

Update

[Francois Teyssier]

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

[Francois Teyssier]

Update of the graph describe in the ATel,
with spectra obtained by Forrest Sims (LISA R1000) and Robin Leadbeater (ALPY600).

TCrB_Flux.PNG (13.82 KiB) Viewed 8710 times

[Francois Teyssier]

A research note about the 2024 November flare is under publication.

David Cujedo obtained a spectrum showing that the system is in a new excited state, with He II, He I.
The observation confirms that short ionized stages could be frequent but not detected due to the cadence of the monitoring.

tcrb.png (20.73 KiB) Viewed 7375 times

[Francois Teyssier]

The RNAAS about the flare detected in November 2024:
T CrB: Detection of a Short Flare in 2024 November
(F. Teyssier, S. N. Shore, F. Sims, R. Leadbeater, J. Guarro Flo, K. Shank, E. Bertrand, and J. R. Foster)

A new flare is decribed in https://www.astronomerstelegram.org/?read=17030
It is obvious in a LISA spectrum secured by David Cujedo:

TCrB_2025-02-06.PNG (44.89 KiB) Viewed 5306 times

T CrB is currently in an intermediate state between low and very high state:
The current orbital cycle is ending (blue dots: AAVSO B, cleaned and daily mean)
The blue line is mean LC (smoothed) for low state
The red one for the very high state 2015-2023)

TCrB_B_c109.PNG (40.56 KiB) Viewed 5306 times

The main purpose of the monitoring is the detection of such flare at various timescales.
Two spectra by week should be a good cadence and daily coverage should be perfect.
Spectra are welcome for inclusion in the database: https://aras-database.github.io/database/tcrb.html

Resolution > 500, good spectral calibration, "good" inst/atmo response are required.
The flux calibration (with V magnitude obtained by the observer during the spectroscopic run (same duration in order to integrate the flickering) is encouraged.
For spectra with short wavelength window:
He II + H beta is recommended
Lhires 2400 l/mm: adopt a line (He II, H beta ...). H alpha (not the best generally speaking) is interesting in the case of T CrB as the observations published in the 80' 90' are essentially equivalent widths of H alpha and they offer a good comparison.

Pronostics and predictions: it is now clear that they failed as expected.
The nova outburst as I explained several time will occur when the accreted mass at the surface of the white dwarf will be sufficient to ignite the CNO cycles and remove the degeneracy. It may happen at any moment from now but it can take years (not a lot of, but several). Nobody knows.

[Robin Leadbeater]

And yet another prediction ATel using my high resolution H alpha spectrum from the ARAS database. (I have no connection with the authors)
https://www.astronomerstelegram.org/?read=17041
"T CrB on the Verge of an Outburst"
I think they should have at least added a question mark

Cheers
Robin