Investigation on the orbital period variations of NN Ser: implications for the hypothetical planets, the Applegate mechanism, and the orbital stability

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 similar to 9.5M(J). 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.

Dergi

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

Yıl

2023

Cilt

526

Sayı

3

Sayfa

4725-4734

ISSN

0035-8711

eISSN

1365-2966

DOI

10.1093/mnras/stad3086

WoS UID

WOS:001163663600018