Detection of superhumps in Gaia16ahk during its ongoing superoutburst

ATel #18045; A. O. Simon (ASPD TShNU of Kyiv), D. Yu. Rusanova (ASPD TShNU of Kyiv), W. Ogloza (UKEN, Cracow; Silesian Planetarium Chorzow), A. Yu. Korosko (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), O. Witkowska (AO of U. Warsaw, PL)), K. Siennicki (AO of U. Warsaw, PL)
on 15 Sep 2026; 18:56 UT
Credential Certification: Andrew Simon (skazhenijandrew@gmail.com)

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We identified Gaia16ahk/AT 2016dun as a promising candidate for an SU UMa-type dwarf nova. Consequently, the occurrence of its next superoutburst was predicted by our Outbursts Alerting System.

Analysis of its long-term light curve revealed, in addition to normal outbursts, brighter and longer outbursts that are likely superoutbursts. The interval between these probable superoutbursts is approximately 335-400 days. The most recent superoutburst began around MJD 60940. Based on this recurrence timescale, the next superoutburst was expected around MJD 61275-61340 (Fig. 1). A new outburst was detected in the ATLAS light curve, starting at MJD 61287, within the expected interval.

Following this detection, time-resolved photometric observations were carried out with the 0.7-m f/4 AZT-8 telescope at the Observational Station Lisnyky of Taras Shevchenko National University of Kyiv and the 0.7-m f/6.5 PlaneWave CDK700 telescope at Planetarium Slaskie in Chorzow to search for superhumps.

Additional photometric observations of Gaia16ahk were carried out with the 60-cm Cassegrain telescope at the Astronomical Observatory of the University of Warsaw in Ostrowik.

To obtain a more accurate determination of the superhump period, we combined the time-resolved observations from four nights after correcting the individual datasets for their photometric zero-point offsets. The resulting combined light curve clearly shows superhumps with a period of 0.07936(4)^d (Fig. 2) and a peak-to-peak amplitude of approximately 0.2^m (Fig. 3). The period was determined using a Lomb-Scargle periodogram implemented with scipy.signal.lombscargle. All materials related to this observation are available on A.O. Simon's personal website.

The detection of superhumps, together with the presence of two distinct types of outbursts in its long-term light curve, provides strong evidence that Gaia16ahk is a newly identified SU UMa-type dwarf nova currently undergoing a superoutburst.

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/Gaia16ahk.

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).