J/A+A/709/A25 AT 2025abao light curves (Reguitti+, 2026)
AT 2025abao: the fourth luminous red nova in M 31.
Reguitti A., Pastorello A., Valerin G., Romanov F.D., Siviero A., Cai Y.-Z.,
Ciroi S., Elias-Rosa N., Iijima T., Kankare E., Koivisto N., Kravtsov T.,
Mason E., Matilainen K., Mura A.C., Ochner P., Reynolds T.M.,
Stritzinger M.D.
<Astron. Astrophys. 709, A25 (2026)>
=2026A&A...709A..25R 2026A&A...709A..25R (SIMBAD/NED BibCode)
ADC_Keywords: Novae ; Photometry
Keywords: techniques: photometric - techniques: spectroscopic -
stars: AGB and post-AGB - binaries: general -
supernovae: individual: AT 2025abao - galaxies: individual: M 31
Abstract:
We present photometric and spectroscopic observations of the luminous
red nova (LRN) AT 2025abao, the fourth discovered in M 31. The LRN,
associated with the AGB star WNTR23bzdiq, was discovered during the
fast rise following the minimum phase. It reached the peak at
g=15.1mag (Mg=-9.5±0.1mag), and then it settled onto a
long-duration plateau in the red bands, lasting 70 days, while it was
slowly linearly declining in the blue bands. The object showed
similarities at peak with the canonical LRNe V838 Monocerotis, V1309
Scorpii, and with the faint and fast-evolving AT 2019zhd, the third
LRN in M31, though the later evolution is different.
Spectroscopically, AT 2025abao evolved as a canonical LRN: the early
spectra present a blue continuum with narrow Balmer lines in emission;
at peak, the spectral continuum has cooled to a yellow colour, with a
photospheric temperature of 6000K. Balmer lines have weakened while
absorption lines from metals (FeI, FeII, ScII, BaII, TiII) have
developed, and in particular broad (FWHM∼700km/s) from the UV CaII H&K
lines. Medium- and high-resolution spectra reveal a counter-P Cygni
absorption profile in Hα. Finally, late time spectra show an
orange continuum (T∼4000-5000K), a return in strength of the Balmer
lines and the formation of molecular absorption bands. AT 2025abao is
the rare case of a LRN with detailed archival information regarding
the progenitor system. For the first time, we obtained the spectral
energy distribution in the infrared of the precursor of a LRN, which
is consistent with that of an M giant/AGB. We propose that the
dichotomy of light curve behaviour in LRNe (two peaks vs. plateau) can
be explained by the extent and H-richness of the common envelope.
Description:
We analysed AT 2025abao, the fourth luminous red nova to occur in the
Andromeda Galaxy. The imaging data utilised in this paper were
obtained with different facilities. Magnitudes, their uncertainties,
and instruments are presented in table.dat.
Objects:
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RA (2000) DE Designation(s)
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00 38 48.62 +40 46 07.6 AT 2025abao
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table.dat 67 706 Photometry table
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Byte-by-byte Description of file: table.dat
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Bytes Format Units Label Explanations
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1- 11 F11.5 d MJD Observation date (MJD)
13- 18 A6 --- Filter Filter (1)
21- 24 A4 --- System Magnitude system, vega or ab
26- 31 F6.3 mag mag Magnitude in Fliter
34- 38 F5.3 mag e_mag Uncertainty in magnitude
42 A1 --- Det [PU] Detection (P=yes, U=no)
44- 67 A24 --- Inst Telescope, Instrument
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Note (1): Filters are BVRI, JHK, ugriz, cyan, orange W1, W2, UVM2, UVW1, UVW2.
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Acknowledgements:
Andrea Reguitti, andrea.reguitti(at)inaf.it
License: CC-BY-4.0 [see https://spdx.org/licenses/]
(End) Patricia Vannier [CDS] 26-Mar-2026