Orbital Period Variation of the Low Mass Ratio Contact Binary HN UMa: O–C Analysis Based on TESS, SuperWASP and Ground Data

The orbital period (OP) variation of the low-mass ratio contact HN Ursae Majoris (UMa) stellar system has been studied in detail for the first time using data from the Transiting Exoplanet Survey Satellite (TESS) and the Super Wide-Angle Search for Planets (SuperWASP) as well as data collected from the literature. We focused on determining the eclipse times (ET) from the light curves (LC) and constructed the O–C diagram from these times. The results obtained indicate the presence of OP variations in the system, where the OP of HN UMa decreases, and this ratio is calculated as dP/dt = –1.74  10-7 days/year. Energy and material transfer from the more mass star to the less mass one was proposed as the reason for the OP decrease, and this ratio was obtained as 3.03  10-8 Mʘ/year. Furthermore, a sinusoidal variation was also observed, and it was hypothesized that a possible third object or magnetic activity could cause this variation. The Js/Jo ratio for HN UMa was calculated as 0.215, and the values of qins and ains were determined as 0.036 and 2.21, respectively. In light of these findings, it can be said that the HN UMa system remains stable for the time being. The findings are likely to contribute to the understanding of the evolutionary processes in low-mass ratio binary systems.