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To: stefano@bicar.it
From: atel@astronomerstelegram.org
Subject: ATel 17932, 17933
Message-Id: <20260801070533.5C9CA2880697@server.astronomerstelegram.org>
Date: Sat, 1 Aug 2026 03:05:33 -0400 (EDT)

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Posted: Within the last 24 hours
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ATEL #17932							     ATEL #17932

Title:	The detection of superhumps confirms Gaia20eud as an SU UMa-type
		dwarf nova
Author:	D. Yu. Rusanova (ASPD TShNU of Kyiv), F.-J. Hambsch (VVS,
		GEOS, BAV), A. O. Simon  (ASPD TShNU of Kyiv), P. J. Mikolajczyk (U.
		Wroclaw/NCBJ, PL), L. Wyrzykowski (U. Warsaw/NCBJ, PL/EASST. eu),
		K. Kotysz (U. Wroclaw/U. Warsaw, PL)
Queries:	andrii.o.simon@gmail.com
Posted:	31 Jul 2026; 21:55 UT
Subjects:Optical, Cataclysmic Variable, Star, Transient, Variables

Our analysis of the BHTom light curve of <a href = 'https://bhtom.space/public/targets/Gaia20eud'>Gaia20eud</a>/AT
2020wjy/ZTF18abmvqfo indicates that the object exhibits two distinct types
of outbursts: normal outbursts and likely superoutbursts. The interval
between these longer outbursts is approximately 300-380 days. The previous
probable superoutburst occurred in August 2025. On 2026 July 25, ZTF observations
detected the object at 17.8m, significantly brighter than its
quiescent magnitude of about 20.2m, indicating the onset of
a new outburst. Given the elapsed time since the previous probable superoutburst
(about 330 days), together with the substantial increase in brightness,
we considered the possibility that the object had entered a superoutburst.

To test this hypothesis, photometric observations were conducted on 2026
July 31 with a C14 f/6.8 telescope at Franz-Josef Hambsch's Remote Observatory
Atacama Desert (ROAD) in Chile to search for superhumps. The data were
uploaded to the <a href = 'https://bh-tom2.astrouw.edu.pl/public/targets/Gaia20eud'>object's
BHTOM page</a> immediately after the observing run. The resulting light
curve (<a href = 'http://aosimon.org.ua/sites/all/files/Gaia20eud_2026-07-31.png'>Fig.
1</a>) clearly shows superhumps. The detection of superhumps confirms Gaia20eud
as an SU UMa-type dwarf nova.

The observations covered MJD 61252.12463-61252.27545 corresponding to approximately
3.6 hours. The superhump period was measured to be 0.0825(7)d
(<a href = 'http://aosimon.org.ua/sites/all/files/Gaia20eud_Periodogram.jpeg'>Fig.
2</a>). The peak-to-peak amplitude is about 0.25m (<a href =
'http://aosimon.org.ua/sites/all/files/Gaia20eud_Zgortka.jpeg'>Fig. 3</a>).
Both values were derived using the Lomb-Scargle periodogram implemented
in SciPy (scipy.signal.lombscargle).

Further observations are strongly encouraged. Observers are invited to
upload their observations to the object's BHTOM page, where all submitted
data are automatically processed: https://bhtom.space/public/targets/Gaia20eud.

BHTOM is based on the open-source <a href = 'https://lco.global/tomtoolkit/'>TOM
Toolkit by LCO</a> and has been developed with funding from the OPTICON-RadioNet
Pilot (ORP) of the European Union's Horizon 2020 research and innovation
programme under grant agreement No <a href = 'https://cordis.europa.eu/project/id/101004719'>101004719</a>
(2021-2025). This project has received funding from the European Union's
Horizon Europe Research and Innovation programme ACME under grant agreement
No <a href = 'https://cordis.europa.eu/project/id/101131928'>101131928</a>
(2024-2028).

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https://www.astronomerstelegram.org/?read=17932
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ATEL #17933							     ATEL #17933

Title:	EP J194531.8-612009: a new magnetic cataclysmic variable
Author:	N. Palivanas (UNIVAP, Brazil), G. J. M. Luna (Conicet/UNAHUR,
		Argentina), E. Martioli (LNA, Brazil), L. Almeida (INPE, Brazil),
		C. V. Rodrigues (INPE, Brazil), I. J. Lima (UNESP, Brazil), D. C.
		Souza (UNIVAP, Brazil), A. S. Oliveira (UNIVAP, Brazil), F. J. Jablonski
		(INPE, Brazil), K. M. G. Silva (Gemini Observatory, Chile), A. C.
		Moreira João (INPE, Brazil), C. Silva (UFC, Brazil)
Queries:	natalia.palivanas@gmail.com
Posted:	1 Aug 2026; 01:24 UT
Subjects:Optical, Binary, Cataclysmic Variable

EP J194531.8-612009 was previously reported by X. H. Tang et al. (ATel
#17926) and P. Balanutsa et al. (ATel #8036) as an X-ray transient and
a cataclysmic variable candidate. TESS photometry revealed a strong periodicity
at 1.897 h (ATel #17930, N. Palivanas et al.), raising the possibility
that the source is a cataclysmic variable below the period gap. Here we
report observations that confirm that this source is a magnetic cataclysmic
variable. We obtained simultaneous polarimetric time series in the g, r,
i, and z bands using the 1.60m Perkin-Elmer telescope and the SPARC4 instrument
at the Pico dos Dias Observatory (managed by Laboratorio Nacional de Astrofisica,
Brazil), on July 29, 2026. The data were collected over approximately 5
hours, with exposure times of 100 and 200 s. They reveal periodic modulation
of the total flux and circular polarization in all bands. The period is
similar to that present in TESS observations, but more data and a proper
analysis are necessary for a good period estimate. The polarization is
always negative, reaching maximum values between 10% and 20%, with the
modulation being more pronounced in the r and i bands. These results suggest
that EP J194531.8-612009 is a magnetic cataclysmic variable of the polar
type, displaying a single active accretion region. This allows us to interpret
the period as the spin period of the white dwarf, which rotates synchronously
to the orbital motion. The transient nature of the system could be related
to the high and low brightness states of this class of interacting binaries.
A thorough analysis of this source will be presented in a paper in preparation.

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