T CrB latest spectra

[Cristian Danescu]

Hello

I started a photometric analysis of this recurring nova a year ago, with some interesting results this year. I found some fairly large amplitude fluctuations in the U band. This type of flicker is not uncommon for such stars. What was a bit unusual (in my humble opinion) was the amplitude of the flicker - about 1 mag.

The most interesting fluctuation (but not the only one) occurred on 05.05.2026. Attached is the photometric graph from that night. Another interesting night was 13.06.2026.

The filter used in this study is not a standard one. The spectrum acquired with it is between B and U, in order to obtain a luminous flux close to the U band, without having problems with the high absorption of U light due to the atmosphere, all with the possibility of obtaining a shorter exposure time.

I wonder if some of you have spectra from T CrB, especially from the U and B parts of the spectrum. I searched the BAA spectrum database and did not find any spectra available for those 2 nights for T CrB.

I think this is a very interesting target for spectra, due to the long-awaited nearby explosion.

Thank you in advance for your help!

Best regards,
Cristiana

[Cristian Danescu]

Cristian not Cristiana, sorry for the typo!...

[Francois Teyssier]

The spectra in ASDB (2120 spectra since 2012) : https://aras-database.github.io/database/tcrb.html

[Francois Teyssier]

Have you performed an autocorrelation test (LombSscargle, Edelson-Krolik..), in order to assure that it is really flickering. The drop in the second graph looks very (too!) smooth

[Christophe Boussin]

Hello Cristian,

I recorded an absolute flux calibrated spectrum of T CrB with my Alpy 600 on June 13, 2026 (resolution of 517, JJ = 2461205.4538 (start of my observation)) and an acquisition time of 60 min (6 x 600 s) :

T CrB on June 13th, 2026 (3700-7396 A)

This spectrum is available on the ARAS database in FITS format.
I measured an average V magnitude of 10.031 (standard deviation = 0.015) over the duration of my data acquisition.

Unfortunately, I didn't record a spectrum of T CrB on May 5, but I hope this one will be useful to you !

Spectroscopically,

Christophe BOUSSIN

[Cristian Danescu]

Have you performed an autocorrelation test (LombSscargle, Edelson-Krolik..), in order to assure that it is really flickering. The drop in the second graph looks very (too!) smooth

I have PERANSO to find periodicity of light curves. PERANSO use Lonb-Scargle method to determine periods in specific cases, but in this context I do not understand what an "autocorelation test" is.

[Francois Teyssier]

The variations in brightness of T CrB (and other symbiotic stars whose main source of energy is accretion) on a short timescale (minutes to hours) produce a flickering phenomenon, the cause of which (as is generally accepted) is accretion through the boundary layer from the disc towards the white dwarf: accretion does not occur at a uniform rate but in bursts. This results in stochastic, quasi-periodic (QPO) variations. Determining whether an observation is quasi-periodic requires an analysis of the signal using autocorrelation.

Here's an analysis on a series (B Band) obtained by Xavier Dupont:

Flickering_TCrB.png (30.05 KiB) Viewed 437 times

The autocorrelation function is more or less a straight line with a negative slope: flickering is confirmed.
A non-variable star would have produced a horizontal line with an y-coordinate of 0. A periodic star would have produced one or more peaks corresponding to the period (as in the example you cite, using Peranso, for instance).
Note: here the graph is plotted against the number of observations; it would be preferable to plot it against frequency.

I hope it's help.