We again used varsim and the NASA Exoplanet Archive to simulate the noise-free transit light curves for each star. The transit modeller within varsim takes as inputs the ephemeris time, orbital period, inclination, eccentricity, argument of periastron, planet mass, and planet radius in addition to the stellar parameters listed in Section 2.2. It implements batman (Kreidberg 2015) for primary transits, spiderman (Louden & Kreidberg 2018) for secondary occultations, and ldtk (Parviainen & Aigrain 2015) for generating PLATO bandpassspecific limb darkening coefficients. Doppler beaming and ellipsoidal variation are implemented in pyastronomy (Czesla et al. 2019), but since the masses of Kepler planets are usually unknown, we assumed zero mass for all planets, thereby removing the impact of these (already minor) effects. We adopted planetary periods, inclinations, eccentricities, and radii from the default parameter sets provided by the NASA Exoplanet Archive. In cases where the argument of periastron was not listed – typically due to the difficulty of measuring this parameter at low eccentricity – we assumed a constant value of 90◦. When eccentricities or inclinations were absent, values of zero and 90◦
10°
0°
75° Galactic Longitude
60° 90° 105°

[Figure: Figure 2. The locations of the sample targets within the LOPN1 PLATO and Kepler fields. The provisional PLATO LOPN1 field is shown in blue, with the darkness of the shaded regions indicating the number of co-pointing cameras, ranging from 6 in the lighter outer regions to 24 in the darker centre. The long-term pointing field of Kepler is shown in red. The positions of the 152 sample stars are shown as circles.]

and 24 cams – 33. For all our simulations, we assume the LOPN1 pointing, with the understanding that the final pointing may change. We note that any change is likely to be small, given the constraints on the minimum ecliptic latitude and the need to be close enough to the galactic plane to cover the required number of sample targets. Thus, it is unlikely that any proposed change would result in missing the Kepler field entirely. We chose to simulate all 152 systems to achieve a statistically powerful sample of TTV planet hosts, despite the considerable computational cost (discussed in Section 2.5). We note that the similarity between the sample host and planet properties and those of the overall Kepler population additionally permits meaningful inferences of the performance of PLATO in following up Kepler targets generally.
were assumed, respectively. For Kepler-103 c, the default stellar and planetary parameters listed in the archive, drawn from Bonomo et al. (2023), yield a transit impact parameter greater than 3, implying a non-transiting geometry. The inclination reported by Bonomo et al. (2023), 87.704+0.12
◦, appears to be a transcription error from the source values reported by Dubber et al. (2019), differing by exactly 2◦. This inconsistency was identified only after the simulations and subsequent analysis had been completed, and Kepler-103 c was therefore excluded from the final sample, reducing the total to 360 planets. Since it is not currently known exactly when PLATO will begin observations of its Northern field (if at all), and a large fraction of our sample planets don’t have ephemeris times listed on the NASA Exoplanet Archive, we uniformly sampled random ephemeris times between zero and each planet’s orbital period. We combined the (potentially multiple) noiseless transit light curves for each star with their stellar variability light curves by multiplying them together to produce two years of intrinsic photometric variability for each system.
−0.055