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From: atel@astronomerstelegram.org
Subject: ATel  17366
Message-Id: <20250901070611.B36D528802CA@server.astronomerstelegram.org>
Date: Mon,  1 Sep 2025 03:06:11 -0400 (EDT)

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Posted: Within the last 24 hours
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ATEL #17366							     ATEL #17366

Title:	Optical photometry and spectroscopy of Nova AT 2025qmf in M31
Author:	A. S. Vinokurov (SAO RAS), O. I. Spiridonova (SAO RAS), A.
		N. Tarasenkov (INASAN, SAI MSU), R. Fidrich (HAA/VSS, Budakeszi, Hungary),
		T. Tordai (HAA/VSS, Budapest, Hungary), D. V. Oparin (SAO RAS), V.
		P. Goranskij (SAO RAS), E. O. Dedov (SAO RAS)
Queries:	vinokurov@sao.ru
Posted:	31 Aug 2025; 19:57 UT
Subjects:Optical, Nova, Transient

We present the results of the photometric monitoring and three spectroscopic
observations of Nova AT 2025qmf carried out between 29 July and 29 August
2025. The data were obtained with seven telescopes: the 0.3m Newtonian
reflextor of T. Tordai; the 0.43m CDK reflector, Alnitak Remote Observatory
at Nerpio; the 0.5m RC500 telescope of the Institute of Astronomy of the
Russian Academy of Sciences (RAS); the 0.51m CDK reflector (iTelescope.net
network), Utah Desert Remote Observatory at Great Basin Desert; the 0.6m
Planewave CDK telescope of Saint Mary's University Burke-Gaffney Telescope;
and the 1m Zeiss-1000 and the 6m BTA telescopes of the Special Astrophysical
Observatory of the RAS.

Analysis of the photometric data indicates that AT 2025qmf remains a bright
source in the optical range, with an average magnitude of B=18.8, V=18.6,
and Rc=18.2. Over the past month, the nova has exhibited several episodes
of brightness increase and decline with an amplitude of approximately 0.7
mag. The spectral energy distribution constructed from the Zeiss-1000 UBVRcIc
photometry (on the night of 27/28 August) shows a strong deviation from
a blackbody spectrum (&chi;<sup>2</sup>/d.o.f.=49 for the best-fit model),
which is in sharp contrast to the satisfactory approximation obtained for
a similar dataset in late July (ATel #17314). The observed excesses in
the U, Rc, and Ic bands suggest a significant contribution from H&alpha;
emission and free-bound radiation.

The first two spectroscopic observations were performed with the Zeiss-1000/MAGIC
using the VPHG600@500 grism (spectral range ~3700-7300A, resolution 10A)
on 29 and 30 July. For each epoch, only two 600s spectra were obtained,
which were co-added to increase the signal-to-noise ratio (S/N). The object's
brightness remained constant within the measurement errors during this
period, Rc = 17.9-18.0 mag. The most prominent emission features in the
combined spectrum are the hydrogen Balmer lines H&alpha; and H&beta;, and
the lines of ionized iron FeII 4924,5018,5169. No clear absorption components
were found, as were observed in the P Cyg profiles of the same spectral
lines a few days later (TNS Classification Report No. 2025-3060). The width
of the most prominent line after correction for the instrumental profile
is FWHM(H&alpha;)~800 km/s; its equivalent width is EW(H&alpha;)~-300A.

The third spectrum was acquired on the night of 21/22 August with the SCORPIO-2
spectrograph on the 6-m SAO RAS telescope. The VPHG1200@540 grism with
a 1" slit was used, covering the 3650-7250A range with a spectral resolution
of about 5A. The total exposure time was 600s. In this spectrum, the H&alpha;
emission component is broader (~1100 km/s), and its equivalent width reaches
nearly -600A. The high S/N of the spectrum allowed the detection of absorption
components in all hydrogen lines up to H&epsilon;. The ejecta velocity,
measured from the blue-edge absorption component relative to the emission
peak of the hydrogen lines, is estimated to be 1700-1900 km/s. The spectrum
also exhibits numerous FeII lines, some of which also show well-defined
P Cyg profiles; the expansion velocity derived from these lines is 1400-1700
km/s. In addition to the aforementioned lines, there are notable features
in the spectrum such as the sodium NaI D doublet and the forbidden oxygen
lines [O I] 5577,6300,6363. The presence of the latter indicates that the
nova has entered the nebular phase.

The work was performed as part of the SAO RAS government contract approved
by the Ministry of Science and Higher Education of the Russian Federation.
Observations with the SAO RAS telescopes are supported by the Ministry
of Science and Higher Education of the Russian Federation. The renovation
of telescope equipment is currently provided within the national project
"Science and Universities". The observations made using the Alnitak Remote
Observatories robotic telescope network, were supported by ARTA program.

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https://www.astronomerstelegram.org/?read=17366
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