Additional Photometry of a Possible Very Slowly Evolving Nova, M31N 2025-12f
ATel #17683; K. Hornoch, H. Kucakova (Astronomical Institute, Ondrejov, Czech Republic), A. W. Shafter (SDSU)
on 16 Feb 2026; 19:35 UT
Distributed as an Instant Email Notice Novae
Credential Certification: Allen W. Shafter (ashafter@sdsu.edu)
Subjects: Optical, Nova, Transient
In ATel #17576 we reported independent discovery of a possible very slowly evolving nova in M31 designated PNV J00432344+4124357 = M31N 2025-12f = AT 2025ajxy, and as ZTF25acghjar by the ZTF.
After discovery, the object brightened very slowly and reached R = 19.0 mag one month later. We also measured its color and found (R-I) = 0.5 +/- 0.2 mag, excluding the possibility that the transient is a Mira-type variable star. We predicted that if it is a nova in M31, it will continue to brighten further like very slowly evolving nova PNV J00423788+4112491 = AT 2022abzg = M31N 2022-09b (see ATel #15831).
To confirm the prediction we followed the object photometrically using the 0.65-m telescope at Ondrejov (D65) yielding the following magnitudes:
Date [UT] | Mag | Err | Filter | Telescope
2026-01-10.779 | 18.9 | 0.2 | R | D65
2026-01-11.683 | 19.0 | 0.25 | R | D65
2026-01-17.912 | 18.8 | 0.15 | R | D65
2026-01-18.688 | 18.8 | 0.2 | R | D65
2026-01-19.705 | 18.7 | 0.3 | R | D65
2026-01-20.928 | 18.9 | 0.15 | R | D65
2026-02-10.718 | 18.9 | 0.1 | R | D65
2026-02-13.850 | 17.83 | 0.10 | R | D65
2026-02-15.796 | 17.6 | 0.1 | R | D65
Based on its photometric evolution, we conclude that M31N 2025-12f is likely a very slowly evolving classical nova in M31. As with other very slow novae, we wouldn't be surprised if this nova has a complex lightcurve with multiple re-brightenings, so follow-up photometric and especially spectroscopic observations of this object are strongly encouraged.
