UT Sep 20, 2025: Photometry of T CrB, V527 And, new guider takes pictures

Michael Richmond
Sep 21, 2025

On the night of Sep 20/21, 2025, under good-to-poor 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.

I was able to take images with the new guide camera -- hooray! I wasn't able to cause it to send corrections to the telescope -- boo!

Note added Sep 23, 2025: Success in sending correcting motions to the telescope. I had to install a driver for the Keyspan USA-19HS serial-to-USB adapter. After doing so, I used the device manager to identify it as port COM7. In MaximDL, I then set the "Guider Settings" to

• Control Via: LX200 Protocol
• COM Port: COM7

I still need to calibrate the new guider, setting the X-speed, Y-speed, and Angle to appropriate values.

The star remains quiescent.

T CrB

This recurrent nova brightens 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:

• Meade 12-inch telescope
• no focal reducer, so working at f/10
• ASI 6200MM CMOS camera
• B-filter 60 sec, V-filter 30 sec
• images binned 4x4
• no guiding
• focus position on 12-inch:
  • V = 0.389 yields FWHM 2.2 pixels at T = 61/16
• custom tracking rate +001

Notes from the night:

• brief periods of light clouds, some clear skies in between
• no Moon
• camera at T = -10 C
• temperatures were chilly: T = 61/16 while focusing, dropping to 45/7 at 04:59 AM
• at start, when taking darks, the camera entered a state in which it cut each exposure short after about 1 second -- but showed exactly the same pixel values as the last legitimate image. I quit MaximDL, unplugged/replugged the camera, and restarted MaximDL. After that, things were fine.
• Connected the new guide camera (ASI120MM Mini) to the main camera via short USB cable. Dome computer now recognizes the guide camera -- maybe because I rebooted it at start of the night. Was able to move the unit to correct position in off-axis guider to bring stars to a focus -- see picture below. Camera takes pictures just fine.

  

• Wasn't able to run autoguider because no signals to move the telescope were passing from guide camera to the telescope. In MaximDL, COM3 seems to be the right port for camera. Tried "Guider Relays" and other protocols, nothing caused telescope drives to move scope. I suspect that perhaps the serial adapter "Keyspan" is at fault: Device Manager shows yellow warning icon on it.

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 clouds in the second half of the run.

The FWHM was pretty steady, but had a large scatter due to the lack of guiding.

The graph below shows changes in the photometric zeropoint of an ensemble solution of the instrumental magnitudes over the course of the run. Note the effect of the clouds.

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 0.008 mag in V, inflated due to trailing. it was 0.009 in B.

The measurements show that the target is still in quiescent phase.

I've submitted these measurements to the AAVSO.

Images of eclipsing binary star V527 And

One of my capstone students is studying the eclipsing binary star V527 And. I acquired some images of it after T CrB reached too large an airmass. The finder telescope shows this on the TV screen when V527 And is in the main telescope's field of view. The two stars at bottom right are good markers.

I acquired 180 pairs of B (60 sec) and V (30 sec) images, all unguided.

                       Start                    End
------------------------------------------------------- 
   EDT    2025 Sep 20  23:25        Sep 21     04:59

   UT     2025 Sep 21  03:25        Sep 21     08:59

   JD       2460939.64294             2460939.87367
-------------------------------------------------------