Non-sinusoidal transit timing variations for the exoplanet HAT-P-12b

Considering the importance of investigating the transit timing variations (TTVs) of transiting exoplanets, we present a follow-up study of HAT-P-12b. We include six new light curves observed between 2011 and 2015 from three different observatories, in association with 25 light curves taken from the published literature. The sample of the data used thus covers a time span of ∼ 10.2 years with a large coverage of epochs (1160) for the transiting events of the exoplanet HAT-P-12b. The light curves are utilized to determine the orbital parameters and conduct an investigation of possible TTVs. The new linear ephemeris shows a large value of reduced χ², i.e. ${\chi }_{{\rm{red}}}^{2}(23)$ = 7.93, and the sinusoidal fitting using the prominent frequency coming from a periodogram shows a reduced χ² around 4. Based on these values and the corresponding O - C diagrams, we suspect the presence of a possible non-sinusoidal TTV in this planetary system. Finally, we find that a scenario with an additional non-transiting exoplanet could explain this TTV with an even smaller reduced χ² value of around 2.