The connection between accretion disk brightness and the white dwarf (WD) reaching the trigger threshold is too weak to be usable, at least for fast timescales. The steady optical light is dominated by the middle of the accretion disk, while the flickering is dominated by closer-in regions of the disk. The inward motions of gas at these disk-radii have timescales of days to months. With ordinary viscocity, a particularly dense clump of mass inside the disk will be smeared out as part of it goes to lower WD-distances, so that its arrival time on the WD will also be smeared out over days-to-months. So we do not expect any sudden dumping of gas landing on the WD. So the increase of the accretion rate onto the WD will be smeared and delayed from seeing any optical brightening in the accretion disk. The accretion rate onto the WD has little immediate connection to the temperature deep within the WD (at the base of the accumulated fresh hydrogen fuel). The reason is that the thermal conduction timescale from the surface to the interior is long. With this diffusion of heat, any thermal pulses from accretion get smeared out further. So there is no ready connection from a brightening in the middle-disk to the temperature at the base of the layer of accumulated fuel. These comments apply for relatively fast variations in the accretion brightness.
For prolonged high states (longer than the various diffusion timescales), the eruption would indeed be more likely to occur during the high state. To use an analogy, a bathtub is more likely to overflow when being filled with the faucet turned on high than when being filled with a leaky dripping faucet. The time when the last gram arrives to push the WD over the trigger threshold for the runaway could happen at either high or low accretion rate. With more mass arriving at the WD during high states (?), the nova eruption is more likely during a high state of accretion.
With this, we can see why T CrB erupts after ten years of being in its pre-eruption high state. Uurgghh, but then why do the eruptions actually wait for a year after the end of that high state (in what is labeled as the pre-eruption dip)? So the last eruption actually happened when T CrB was in its low state. And why did the high state start and stop? And why did the start and stop times in 2015 and 2024 match the start and stop times in the previous eruption (1935 and 1945)? Such matching shows that the high states in T CrB are not random, but involve a nearly-deterministic scenario that we have not yet know or understand.
Interesting. I presume the very nice B & V light curve data the last plot in the Tautenberg report mentioned by Brian came from the AAVSO!
(DEY)
Waiting for T CrB to erupt is like watching a soap opera! Itās great that there are so many observations of T CrB prior to eruption because it will be interesting to look at the activity just prior to eruption and try to see a trigger.
One more T CrB item from the x-ray angle on last nightās astro-ph:
\Brian
Indeed, the strength and profile of the emission lines from the symbiotic activity (such as hydrogen and helium) depend highly on the orbital phase, which induces a 227d periodic modulation of the spectral profile. Currently, we are seeing the system with the white dwarf in front of the giant; hence, the emission lines are expected to be stronger and narrower. Monitoring the emissions lines at different excitation energies allows us to see the system from different vantage points and, therefore, to probe various parts of the accretion disk, such as the bright spot at the impact of the stream and the diskās outer edge. See, for example, our recent analysis Resolving the mass transfer in the symbiotic recurrent nova T CoronƦ Borealis, where six different interaction sites were mapped from the optical lines of T CrB, as sketched in Fig. 8 from the paper:
So, the increase in the strength of Halpha is not uncommon, given the orbital phase and the fact that the emission line strength correlates with the B-band mean magnitude. What is more intriguing is that the emission line strength is more pronounced than what we observed precisely one orbital cycle before, meaning that the disk has left the bottom of the eruption dip. This hints at an increased disk activity and temperature, which has been strongly reduced since mid-2023. However, the strength of any emission lines is still less than that of the systems exhibited during the superactive phase from 2015 to 2023.
Letās wait and see what the system is up to
A T CrB observation at visual magnitude 5.8 was reported to the AAVSO today and may have been distributed to MyNewsFlash subscribers. It was a typographical error and should have been <5.8. Later observations from overnight show T CrB still down as of 20 February 2025.
Thanks, and good observing,
Elizabeth Waagen, AAVSO HQ
Hello everybody!
Hereās a detrended light curve of the past six months (+) of T CrB (Johnson B filter observations - AAVSO).
The magenta line is a 12 degree polynomial fit of the data.
Cheers!
Enrique Boeneker
(BETB)
Hey again!
I was reprimanded by a couple of professional astronomers due to the fact I fitted the 12 degree polynomial in the de-trended light curve of T CrBā¦ and they are right. After all, it does not add any information at all, and might lead to confusion. So I apologize to all of you. Sometimes me being playful takes me to places I should not have to go. And please, bear with me, I am a slow learner. 
Cheers!
Enrique Boeneker
(BETB)
A 12th-order fit has no physical meaning per se but it did a decent job of ādetrendingā to reveal the overall scatter, individual observer bias, outliers, etc. in the observations over the fitted interval. So perhaps a bit useful from that point-of-view.
Jim (DEY)
Perhaps there is a āteachable momentā here in noting that when one fits polynomials to data, one must be able to derive uncertainties on the coefficients (not all software will do so). It is customary to ignore higher-order terms unless they are at least 2x (or 2.5x) smaller than the coefficient involved. Some instructive guidance in this regard can be found in a paper by Taylor & Joner:
ā¦which is rather dense but highly instructive. See their text section 3.2 about over-fitting to data.
\Brian
I wrote (poorly): āIt is customary to ignore higher-order terms unless they are at least 2x (or 2.5x) smaller than the coefficient involved.ā I intended to say that the errors on the coefficients should be at least 2x smaller than the coefficients themselves. Sorry for the mixed-up wording.
\Brian
Wow. I canāt believe it. I just came across your paper here. Iām just an amateur, but back in May 2024, after absorbing quite a bit of info on T CRB, I did some back of envelope scratching and came to very nearly the same dates you did. I even typed up a short āpaperā and saved it for future reference. I gave a short lecture at our club meeting, that these are dates to be particularly watchful of.
I didnāt seriously consider the third body. I was thinking more along the lines of a 70 pulsation period of the RG as a trigger for the high phase.
Keeping up with the latest literaature on T CrB, I note the following from astro-ph:
Along with new radial-velocity data, the thing I like best about the paper is the rather complete listing of recent literature in context, including photometry, spectroscopy, and other relevant results.
\Brian
Getting up to look at 5 or 6am most mornings now from South Australia. 
Now that is a scientific paperānice find Brian!. Very reference dense and will be great for detailed readingā¦ to check every reference could take a long time tho but maybe my AI could do it in short order!
A decent book is by Grant Foster, āAnalyzing Light Curves: A Practical Guideā (2010). I didnāt check but presume it is still in print and available. The book covers and is the basis of much of what is inside the AAVSOās VStar software.
Excel, Microsoft 365, will produce the coefficient standard errors and many other roll-up type statistics for linear regressions if you download/enable the Data Analysis Tools. Higher order fitting can be done in excel via downloading and enabling a free tool add-on called the Real Statistics Resource Pack. However, I have not used this 3rd party tool at this point in MS 365 but it looks good!
Usually an F or t-test is used to decide if adding higher orders terms to a regression are āsignificantā.
Jim (DEY)
If you,have your short āpaperā , can you send it to me ?
Jean Schneider
https://luth7.obspm.fr
Today I was looking at T CrB B filter observations. It is perhaps interesting to note that the current magnitude of about 11.2B on average is an intermediate level compared to the last 25 years I looked at. At low-state before 2015 January the B level is about 11.6B. The high-state attained about 10.8B. The ādipā reached the low-state level of about 11.6B and now mid 2025 March T CrB is at an intermediate magnitude of about 11.2B.
Jim (DEY)
Just showed up on Astronomers Telegram.
@DEY_VAR if I recall correctly, there was a paper (or maybe an ATEL) that explained the pre-eruption dip that Brad, Elizabeth, and I announced in July 2024 as a relatively short-lived increase in dust formation.
@Alan_Webb Iām no surprised to see that result. From reviewing spectra coming in to AVSpec, it seems that the H and He emission lines are correlated with orbital phase. They have been relatively strong for about a month now and were in a similar condition about 227 days prior.
Brian
On clear and dry nights, I now have my Seestar S50 smart telescope monitoring T CrB while Iām sleeping. In parallel to the Seestar executing the āobservation planā (a relatively new feature in the Seestar App), I have my own scripts (running an a Raspberry Pi in the same LAN) that are doing some rough quick-look-photometry and will try to wake me up when thresholds of brighness are crossed by T CrB. Currently set to 9.5 mag (TG).
The project is still in beta test and Iām fine tuning parameters, but if anyone wants to play around with the scripts, feel free to do so: GitHub - Bikeman/SeestarPhotometricWatchdog: A collection of simple scripts to perform on-the-fly photometry with the ZWO Seestar series telescopes in order to spot variabilities in real-time, e.g. for catching the erruption of T CrB
Cheers
HBE