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From: atel@astronomerstelegram.org
Subject: ATel  17361, 17362
Message-Id: <20250828071146.C07CA2880144@server.astronomerstelegram.org>
Date: Thu, 28 Aug 2025 03:11:46 -0400 (EDT)

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Posted: Within the last 24 hours
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ATEL #17361							     ATEL #17361

Title:	Discovery, photometry and spectroscopic classification of SN
		2025umq as Type Ia supernova
Author:	Filipp Romanov (amateur astronomer, complimentary member of
		the AAVSO), Jacob Wise (LJMU), Christoffer Fremling (Caltech)
Queries:	filipp.romanov.27.04.1997@gmail.com
Posted:	27 Aug 2025; 21:06 UT
Subjects:Optical, Supernovae, Transient

On 2025-08-17 (midtime of the first image 17.627016 UT) F. D. Romanov discovered
the supernova (SN) candidate in the galaxy SDSS J004819.14+075856.8 at
5x300 sec. images (at a distance of approximately 12 arcsec. from the edges
of the images) obtained with the Luminance filter at his request remotely
using the telescope T59 (0.51-m f/6.8 reflector + CCD) of iTelescope.Net
in Siding Spring Observatory (Australia); it was designated AT 2025umq
(TNS) = PSN J00481888+0759006 (CBAT TOCP). The measured magnitude was 19.6
+/- 0.3 in the stacked image compared to G magnitudes of nearby stars from
Gaia DR2 catalogue (Gaia Collaboration et al. 2018), measured position
(J2000.0): 00:48:18.884 +07:59:00.56.

F. D. Romanov remotely observed AT 2025umq using the IO:O camera on the
2-m Liverpool Telescope (Steele et al. 2004) with Sloan g', r' and i' filters
and measured the magnitudes (aperture photometry):

JD / Magnitude / Error / Filter / Exposure

2460910.6791454400 20.74 0.10 g' 2x60s.

2460911.6596276271 21.07 0.15 g' 3x60s.

2460906.6590004745 20.38 0.13 r' 5x60s.

2460910.6815234604 20.63 0.15 r' 2x60s.

2460911.6624643635 20.49 0.12 r' 3x60s.

2460910.6838803818 20.66 0.13 i' 2x60s.

2460911.6652745022 21.08 0.15 i' 3x60s.

The magnitudes of comparison stars were taken from Pan-STARRS DR1 catalogue
(Chambers et al. 2016). Romanov also measured the position from the Liverpool
Telescope photographs: 00:48:18.875 +07:59:00.67.

The spectrum of AT 2025umq (PSN J00481888+0759006) was obtained during
3400 seconds (PATAG proposal AZ22A01; PI: F. Romanov) on 2025-08-20, midtime
03:06:46 UT, remotely using the low resolution (approximately R = 350 =
18 Å) SPRAT (Piascik et al. 2014) spectrograph on the Liverpool Telescope
with the red-optimised mode (grating option).

The same image shows spectra of both the SN candidate and SDSS J004819.14+075856.8:
the host galaxy spectrum https://www.wis-tns.org/system/files/uploaded/F.%20D.%20Romanov/tns_2025umq_atrep_21875_F._D._Romanov.png
shows H-alpha emission, and also sodium (Na D) absorption features, this
allowed to narrow down the redshift to z = 0.159.

Comparison (using the software package "Next Generation SuperFit" (NGSF):
Goldwasser et al. 2022) of the spectrum of AT 2025umq to templates of previously
classified transients at a redshift of z = 0.159, finding it to be consistent
with a fading SN Ia: the typical feature caused by high velocity iron is
visible between approximately 5000 A and 5500 A; and silicon absorption
feature is visible at approximately 7100 A.

The ZTF light curve (presented online https://alerce.online/object/ZTF25abexekl,
but photometric data were not reported to TNS) shows the first g-band detection
on 2025-07-25 and the peak magnitude of about +20 near August 10, 2025.
Calculation with K-correction shows the absolute magnitude of about -19.6,
this also matches a SN Ia.

Based on the above, we classify AT 2025umq as Type Ia supernova in the
galaxy SDSS J004819.14+075856.8. The spectrum of SN 2025umq has been uploaded
to the Transient Name Server: https://www.wis-tns.org/system/files/uploaded/F.%20D.%20Romanov/tns_2025umq_atrep_21875_F._D._Romanov_0.png

Stacked (3x60 sec. images with g', r' and i' filters; 0.30"/px, north is
up, east is left) color image of SN 2025umq for 2025-08-24 03:53:55 UT
midtime is available at the link: https://www.wis-tns.org/system/files/uploaded/F.%20D.%20Romanov/tns_2025umq_atrep_267781_F._D._Romanov.jpg

F. D. Romanov is grateful to iTelescope.Net for giving him some complimentary
points for observing time with their remote telescopes.The Liverpool Telescope
is operated on the island of La Palma by Liverpool John Moores University
(LJMU) in the Spanish Observatorio del Roque de los Muchachos of the Instituto
de Astrofisica de Canarias with financial support from the UK Science and
Technology Facilities Council.

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Password Certification: Christoffer Fremling (fremling@caltech.edu)
https://www.astronomerstelegram.org/?read=17361
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ATEL #17362							     ATEL #17362

Title:	The Depletion of Carbon-Bearing Species in Comet ATLAS (2025
		K1)
Author:	David Schleicher (Lowell Observatory)
Queries:	dgs@lowell.edu
Posted:	27 Aug 2025; 21:49 UT
Subjects:Optical, Comet

I obtained 2 sets of narrowband photoelectric photometry for dynamically
new  
Comet ATLAS (2025 K1) on 2025 August 19 (r=1.25 AU) using the Hall 42-inch

(1.1-m) telescope at Lowell Observatory. Both sets utilized a 97 arcsec
aperture,  
yielding the following mean gas production rates using our standard methodologies

and parameters (cf. Schleicher & Bair 2011, AJ 141, #177):

log Q(OH; Haser) = 27.58 
log Q(H2O; vectorial) = 27.66 
log Q(CN) = 23.86 
log Q(C2) = 24.21 
log Q(C3) = 23.11 (with large uncertainty) 
log Q(NH) = 25.21 
log Afrho = 1.6

Note that all of the carbon-bearing species, including CN, are unusually
low as  
compared to OH, based on our Lowell database of comet compositions (A'Hearn
et al.  
1995; Schleicher and Bair 2016: AAS/DPS Meeting #48, paper #308.04).  
We are aware of only two comets having a lower CN-to-OH ratio - Comet

Yanaka (1988r = 1988 Y1), for which Fink (1992) measured a depletion of

CN-to-water of more than a factor of 25, and Comet 96P/Machholz 1, for
which  
Schleicher (2008) measured a depletion by a factor of 72 as compared to
the  
mean value for typical comets. The depletions of C2 and C3 in 2025 K1 are

large when compared to OH but not when compared to CN. The NH-to-OH ratio
is  
normal, while the dust-to-gas ratio is low but not unusual.

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Password Certification: David Schleicher (dgs@lowell.edu)
https://www.astronomerstelegram.org/?read=17362
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