On the night of Jun 16/17, 2025, under fair conditions, I acquired images of the recurrent nova T CrB. This star undergoes outbursts at long intervals of 80 years or so. Its next outburst is predicted to occur soon (but then again, it was also predicted to occur during 2024), and so I've joined the crowd who are monitoring it.
Tonight featured a brief moment of excitement when I noticed a (very) small increase in T CrB's brightness, but it turned out to be a particularly large example of the short ups-and-downs of this system. Rats.
This recurrent nova brightens from by about 8 magnitudes (!), from V = 10 to about V = 2, around every 80 years. Will we see another outburst THIS summer?
These observations involved:
Notes from the night:
The picture below shows a cropped image of the field of T CrB from Jun 14/15, 2024. The field of view is about 20 arcminutes across.
I've marked the location of several comparison stars, with magnitudes and names taken from the AAVSO's table X40237AAS. Note that the magnitudes listed for stars "A" and "B" have changed from the ones I listed in last year's notes.
star name B V
------------------------------------------------------
A 000-BJS-901 11.096 10.554
B 000-BBW-805 11.779 11.166
C 000-BPC-198 13.049 12.336
--------------------------------------------------------------------------
When the target is centered, the finder TV shows this field:
Here's the sky background over the course of the run. Note the brief period of clouds early.
The FWHM rose a bit over the course of the run -- that's a bit unusual.
The graph below shows changes in the photometric zeropoint of an ensemble solution of the instrumental magnitudes over the course of the run. The early period of clouds featured about 0.8 mag of extinction; not a small amount.
Using aperture photometry with a radius of 7 pixels in V filter (binned 4x4, each pixel is 1.036 arcsec, so a radius of 7.3 arcsec), and 7 pixels in B filter (binned 4x4, each pixel is 1.036 arcsec, so a radius of 7.3 arcsec), I measured the instrumental magnitudes of a number of reference stars and the target. Following the procedures outlined by Kent Honeycutt's article on inhomogeneous ensemble photometry, I used all stars available in each image to define a reference frame, and measured each star against this frame.
Sigma-vs-mag plots show that the floor in V-band was about 0.005 mag, which is good. In B-band, it was 0.006 mag.
The measurements show that the target is still quiescent.
I've submitted these measurements to the AAVSO.