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We present 36 new mid-eclipse times obtained between 2017 and 2023 using the T100 telescope in Turkey, extending the time span of the O − C diagram to 25 yr. Once again, these new observations show significant deviations from previous published models that were able to explain the observed variations of the binary period. We investigate two plausible explanations for this variability: the light travel time (LTT) effect due to the presence of one or two invisible low-mass (planetary) companion(s) in distant circumbinary orbits; other mechanisms, like e.g. the Applegate mechanism, associated with the magnetic cycles of the M-dwarf component of the WD + dM binary. Through Markov Chain Monte Carlo analyses, we demonstrate that the observed O − C variability can be explained by the presence of a planet with a minimum mass of ∼9.5 MJ. This circumbinary planet orbits around the binary system with a period of about 19.5 yr, maintaining a stable orbit for a timeline of 10 Myr. By adding a weak LTT signal from a secondary hypothetical planet we achieve statistically better results. However, the orbits of the bodies in a two-planet system remain stable only for a small range of the parameter space. The energy required to power the Applegate and other Applegate-like mechanisms is too high to explain the period variations observed. Thus, on the one hand there is substantial evidence supporting the existence of a planet in the NN Ser system, but on the other hand there are also compelling indications that cast doubt on the existence of a second hypothetical planet. [ABSTRACT FROM AUTHOR]

As a result of various studies, it has been determined that several post-common envelope eclipsing binaries have variations in their orbital periods. These variations are thought to be caused by the existence of additional bodies in the system (hypothetical stars or planets) and/or other physical effects (such as angular momentum loss, magnetic activity) of the binary system. It is also known that the sdB+M eclipsing system NY Vir has shown such variations in the last decade, indicating additional objects and/or other physical effects. In this work, we present 51 new eclipse times for this system, which extend the time-span of it is O − C diagram by about 3 yr, obtained between 2015 and 2021 using two different telescopes in Turkey. The data obtained in the last 3 yr show a new trend in the O − C diagram differently from the predictions of the previous studies. Our model is consistent with the new O − C diagram, which is statistically well fitted with the quadratic term and the additional two planets with masses of M 3 = 2.74  M Jup and M 4 = 5.59  M Jup. However, the orbital period variation can also be related to magnetic activity. In order to better understand the mechanism causing the changes in the orbital period, new observation data are needed that will show at least one full cycle of the change in the O − C diagram. [ABSTRACT FROM AUTHOR]