SU UMa-type Dwarf Nova MASTER OT J212624.16+253827.2 in the Period Gap: Orbital Period and Negative Superhumps

The results of the analysis of photometric observations of the long-period SU UMa-type dwarf nova MASTER OT J212624.16+253827.2 are presented based on the ZTF, ATLAS, GAIA, and ASAS-SN data obtained in 2018–2023 (HJD 2 456 772–2 460 568) and the Crimean Astrophysical Observatory obtained in 2023–2024 (HJD 2 460 199–2 460 576) at different stages of outburst activity. We found that this observation interval is notable for variations in the supercycle and cycle of the dwarf nova, equal to $${{146}^{d}}{\kern 1pt} - {\kern 1pt} {{184}^{d}}$$ and $${{12}^{d}}{\kern 1pt} - {\kern 1pt} {{37}^{d}}$$ , respectively. For the first time, we determined the orbital period equal to $${{0.0865044(2)}^{d}}$$ , which dominated in the 2018–2023 (HJD 2 458 228–2 458 836) quiescence and the period of negative superhumps $${{0.083}^{d}}{\kern 1pt} - {\kern 1pt} {{0.084}^{d}}$$ , which dominated in 2023–2024 (HJD 2460199–2460576) quiescence. The estimated mass ratio of the system components is 0.21(2).