[vsnet-alert 24375] ASASSN-V J205457.73+515731.9 (ATEL)

[Taichi Kato]

ASASSN-V J205457.73+515731.9 (ATEL)

   Likely new VY Scl variable.  The variability was
reported by ATLAS earlier (ATO J313.7404+51.9588).
Now slowly fading.

===

ATEL #13824                                                          ATEL #13824

Title:  ASAS-SN Discovery of an Unusually Luminous Cataclysmic Variable
                Candidate Undergoing a Dimming Episode
Author: T. Jayasinghe,  K. Z. Stanek, C. S. Kochanek, Z. Way, P. Vallely,
                C. Basinger, T. A. Thompson (OSU), B. J. Shappee (Univ. of Hawai
i),
                T. W.-S. Holoien (Carnegie Observatories), J. L. Prieto (Diego P
ortales;
                MAS), Subo Dong (KIAA-PKU)
Queries:        jayasinghearachchilage.1 at osu.edu
Posted: 22 Jun 2020; 22:32 UT
Subjects:Optical, Cataclysmic Variable, Star

During the ongoing All Sky Automated Survey for SuperNovae (ASAS-SN, Shappee
et al. 2014, Kochanek et al. 2017), using data from the quadruple 14-cm
"Brutus", and "Leavitt", telescopes, we identified a likely cataclysmic
variable star undergoing a dimming episode. The ASAS-SN variable source
ASASSN-V J205457.73+515731.9 (position from Gaia DR2, source_id=2170074115128375
680,
d~564 pc, R~0.53 R_sun, Teff~7489 K, L~0.78 L_sun) was first observed by
ASAS-SN on UT 2015-03-02. The Gaia temperature estimate is indicative of
a hot companion/accretion disk. The line of sight extinction from the Bayestar19
dust maps (Green et al. 2019) to ASASSN-V J205457.73+515731.9 is significant
(A_V~1.3 mag, A_g~1.7 mag) as it is located in the Galactic disk with (l,b)~(90.
895,4.452).
Presently, ASASSN-V J205457.73+515731.9 has more than ~2300 data points
over a baseline of ~1930 days. 

ASASSN-V J205457.73+515731.9 has <a href=https://asas-sn.osu.edu/light_curves/90
07926c-f1ac-4dc5-b9e9-f4eb60b9f529>
a quiescent mean magnitude of g~13.8 (V~13.6)</a>. A dimming episode with
an ingress on UT 2017-03-27 was observed in the V-band, with the star reaching
a minimum brightness of V~13.8 at UT 2017-04-08, and returning to its quiescent
state over a total duration of t~30 days. ASASSN-V J205457.73+515731.9
is <a href=https://asas-sn.osu.edu/light_curves/ea2280a4-623a-44ec-87df-b7f23e4b
0920>
currently undergoing a dimming episode</a>, beginning on UT 2020-05-28
and is at g~14.4 as of UT 2020-06-22. The current dimming episode is slower
and deeper than the previously observed event in the V-band data. We do
not see evidence for significant periodic variability when the system is
quiescent.

Such dimming episodes are characteristic of VY Scl stars and are the results
of low mass transfer episodes from the companion star (Leach 1999). However,
ASASSN-V J205457.73+515731.9 is more luminous than typical CVs, with M_V~4.8
mag and M_g~5.0 mag. Further photometric and spectroscopic observations
are encouraged.