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The abundance of planets with orbital periods of a few to tens of dayssuggests that exoplanets experience complex dynamical histories. Planets inyoung stellar clusters or associations have well-constrained ages and thereforeprovide an opportunity to explore the dynamical evolution of exoplanets. K2-25bis a Neptune-sized planet in an eccentric, 3.48 day orbit around an M4.5 dwarfstar in the Hyades cluster (650 Myr). In order to investigate its non-zeroeccentricity and tight orbit, we analyze transit timing variations (TTVs) whichcould reveal clues to the migration processes that may have acted on theplanet. We obtain 12 non-consecutive transits using the MEarth Observatoriesand long-term photometric monitoring, which we combine with 10 transits fromthe Spitzer Space Telescope and 20 transits from K2. Tables of MEarthphotometry accompany this work. We fit each transit lightcurve independently.We first investigate whether inhomogeneities on the stellar surface (such asspots or plages) are differentially affecting our transit observations. Themeasured transit depth does not vary significantly between transits, though wesee some deviations from the fiducial transit model. We then looked for TTVs asevidence of a non-transiting perturber in the system. We find no evidence for >1 $M_\oplus$ companions within a 2:1 period ratio, or for > 5 $M_\oplus$planets within a 7:2 period ratio.

The young planetary system K2-25: constraints on companions and starspots