Gaia20dsz: superhumps detected during a new superoutburst

ATel #18102; D. Yu. Rusanova (ASPD TShNU of Kyiv, Ukraine), A. O. Simon (ASPD TShNU of Kyiv, Ukraine), A. Yu. Korosko (ASPD TShNU of Kyiv, Ukraine), S. Kurowski (Jagiellonian University, PL/SOA Bolecina, Poland), K. Siennicki (U. Warsaw, Poland), W. Skrobacz (U. Warsaw, Poland), V. V. Vasylenko (ASPD TShNU of Kyiv, Ukraine), S. Dufoer (VVS, Belgium), P. J. Mikolajczyk (U. Wroclaw/NCBJ, Poland), L. Wyrzykowski (U. Warsaw/NCBJ, PL/EASST. eu, Poland), K. Kotysz (U. Wroclaw/U. Warsaw, Poland)
on 12 Oct 2026; 18:58 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Andrew Simon (skazhenijandrew@gmail.com)

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The next superoutburst of Gaia20dsz/AT 2020rgw was predicted by our Outbursts Alerting System to occur within MJD 61309-61324. Based on this prediction, we initiated time-resolved photometric observations to monitor the expected outburst and search for superhumps.

Gaia20dsz has a previously measured orbital period of 0.0582(1)^d, determined during quiescence (Paterson et al. 2019, MNRAS, 486, 2422-2434; doi: 10.1093/mnras/stz1018). Its long-term light curve shows superoutbursts lasting approximately 11-13 days and recurring at intervals of about 70-85 days, with 6-9 normal outbursts occurring between consecutive superoutbursts.

Time-resolved photometric observations were obtained using the 0.5-m OAUJ Cassegrain Telescope, the 0.6-m Cassegrain telescope at the Astronomical Observatory of the University of Warsaw in Ostrowik, the 0.4-m telescope of the EEye Astronomical Complex and the 0.7-m f/4 AZT-8 telescope at the Observational Station Lisnyky of Taras Shevchenko National University of Kyiv.

Observations obtained on MJD 61317, 61319, 61320, 61322, 61323 and 61324 reveal clear periodic brightness modulations. A Lomb-Scargle analysis of the combined data yields a dominant period of 0.0636(11)d (Fig. 1). The modulations have a peak-to-peak amplitude of approximately 0.1^m (Fig. 2). Additional materials related to this observing campaign are available on A.O. Simon's personal website.

The presence of normal outbursts and superoutbursts, together with the detection of superhump-like modulations, supports the classification of Gaia20dsz as an SU UMa-type dwarf nova. Its unusually short supercycle of approximately 70-85 days and frequent normal outbursts suggest similarities to systems of the ER UMa subtype, although its relatively low superoutburst duty cycle is not typical of this subtype.

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/Gaia20dsz.

BHTOM is based on the open-source TOM Toolkit by LCO 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 101004719 (2021-2025). This project has received funding from the European Union's Horizon Europe Research and Innovation programme ACME under grant agreement No 101131928 (2024-2028).