Changes in the Period of Negative Superhumps of Type SU UMa Dwarf Novae. II. NY Her (2017 and 2020)

Photometric studies of the type SU UMa dwarf nova NY Her were made during 2017 and 2020 at the Crimean Astrophysical Observatory and at the Sanglokh Observatory over a total of 77 nights. These observations covered two superoutbursts, four normal outbursts, and the quiescent state between them. In 2017 the supercycle was 62 days, and the cycle, 13-14 days. Positive superhumps with an average period of 0.07594 days and a variable amplitude not exceeding 0m.15 were observed during the superoutbursts. In the quiescent state between outbursts, as well as in the ascending and descending branches of the normal outbursts, negative superhumps with an average period of 0.071269 days were recorded. Their amplitude ranged over 0m.3-1m.5 in the quiescent state. The period of the negative superhumps manifested cyclical increases between normal outbursts, which is consistent with the prediction of a cyclical change in the radius of the accretion disk in terms of the thermal-tidal theory of the instability.