Photometric Follow-up of the Nova Candidate AT 2025qmf in M31

ATel #17314; Vinokurov A. S. (SAO RAS), Dedov E. O. (SAO RAS), Lopatin K. N. (UrFU), Spiridonova O. I. (SAO RAS), Goranskij V. P. (SAO RAS)
on 30 Jul 2025; 19:03 UT
Credential Certification: Alexander Vinokurov (vinokurov@sao.ru)

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We continue photometric observations of the nova candidate AT 2025qmf, discovered by Robert Fidrich in the field of M31 on 2025 July 6 (TNS Astronomical Transient Report No. 261717). Direct imaging was carried out immediately before or during morning twilight using the 1-m Zeiss-1000 telescope at SAO RAS in Johnson-Cousins B, V and Rc filters, with the wavelength coverage extended to U and Ic on the fifth night. Atmospheric transparency was relatively good during observations, with seeing varying between 2" and 3.5".

Aperture photometry was conducted using six SDSS DR16 catalog sources within 162" of AT 2025qmf as photometric standards for calibration to the VEGAMAG system. The AB ugriz magnitudes of the reference stars were converted to the Johnson-Cousins system using PySynphot routines. The photometric results are presented in the table below; the reported errors include both the statistical uncertainty in the object's flux measurement and the calibration error based on the six reference stars.

Compared to previous measurements (18.50 ± 0.11 in Johnson R at MJD = 60866.14, ATel #17285), the object brightened by 0.72 mag (converted to Johnson R) by MJD = 60871.99, then slightly faded, stabilizing at Rc = 18.0 over the past week. The blackbody fit of the spectral energy distribution obtained on July 27 (MJD = 60883.95) yields an estimated color temperature of ~9500 K, assuming Galactic extinction A_V(G) = 0.2. The latter assumption is quite reasonable, given the location of AT 2025qmf on the outskirts of the M31 disk, where significant additional extinction is unlikely.

To investigate a possible progenitor, we performed relative astrometry between our Rc-band data and an archival SDSS r-band image using nine reference stars within 100" of the target. The corrected source coordinates are R.A. = 00:39:31.317, Dec. = +41:11:28.02, with 1σ uncertainties of 0.10" in R.A. and 0.03" in Dec. No sources are detected within the 3σ error box of AT 2025qmf in the SDSS image, with a limiting magnitude of r = 23.3 mag, implying an outburst amplitude of >5.5 mag based on currently published measurements. The nearest detected source lies 1.3" away, with r = 22.69 ± 0.21. Interestingly, a planetary nebula candidate (Merrett et al. 2006, MNRAS, 369, 120) is located at a similar offset, with a radial velocity (V_r = -491.9 km/s) consistent with M31’s velocity field.

As AT 2025qmf remains bright, we encourage spectroscopic follow-up for classification.

 
MJD | Filter | Total exp., s | Mag  
  
 
60871.99 | B  |  600  |  18.275 ± 0.023 
  
         | V  |  600  |  18.088 ± 0.021 
  
         | Rc |  600  |  17.849 ± 0.015 
  
60874.03 | B  |  300  |  18.24 ± 0.05 
  
         | V  |  250  |  17.98 ± 0.03 
 
         | Rc |  200  |  17.869 ± 0.018 
  
60877.03 | B  |  300  |  18.37 ± 0.13 
  
         | V  |  250  |  18.32 ± 0.12 
 
         | Rc |  200  |  18.03 ± 0.05 
 
60880.03 | B  |  300  |  18.36 ± 0.04 
  
         | V  |  200  |  18.15 ± 0.04 
 
         | Rc |  200  |  17.98 ± 0.09 
 
60883.95 | U  |  600  |  17.775 ± 0.023 
 
         | B  |  500  |  18.411 ± 0.015 
  
         | V  |  300  |  18.228 ± 0.016 
 
         | Rc |  300  |  17.978 ± 0.014 
 
         | Ic |  300  |  17.776 ± 0.024