ExoClock Project. II. A Large-scale Integrated Study with 180 Updated Exoplanet Ephemerides

Abstract

The ExoClock project is an inclusive, integrated, and interactive platform that was developed to monitor the ephemerides of the Ariel targets to increase the mission efficiency. The project makes the best use of all available resources, i.e., observations from ground telescopes, midtime values from the literature, and finally, observations from space instruments. Currently, the ExoClock network includes 280 participants with telescopes capable of observing 85% of the currently known Ariel candidate targets. This work includes the results of ∼1600 observations obtained up to 2020 December 31 from the ExoClock network. These data in combination with ∼2350 midtime values collected from the literature are used to update the ephemerides of 180 planets. The analysis shows that 40% of the updated ephemerides will have an impact on future scheduling as either they have a significantly improved precision or they have revealed biases in the old ephemerides. With the new observations, the observing coverage and rate for half of the planets in the sample has been doubled or more. Finally, from a population perspective, we identify that the differences in the 2028 predictions between the old and the new ephemerides have an STD that is double what is expected from Gaussian uncertainties. These findings have implications for planning future observations, where we will need to account for drifts potentially greater than the prediction uncertainties. The updated ephemerides are open and accessible to the wider exoplanet community both from our Open Science Framework repository and our website.

Spatially-resolving the terminator: Variation of Fe, temperature and winds in WASP-76 b across planetary limbs and orbital phase

“…The Δ𝑉 sys values are dependent on the orbital period and transit time centre, but by propagating the uncertainties reported in Ehrenreich et al (2020), we find that Δ𝑉 sys changes by at most ∼0.5 km/s. By using other recently published precise orbital values (Kokori et al 2022;Ivshina & Winn 2022), we also find consistent results to within the uncertainties and ∼1 km/s. Therefore, any red-or blue-shift of the spectrum indicates the presence of a wind and cannot be explained by variations in orbital parameters.…”

Evidence of Long-term Period Variations in the Exoplanet Transit Database (ETD)

“…However, given their large transit depth, high-quality observations of HJs around bright stars can be achieved with relatively modest equipment. As such, citizen astronomers have for decades been able to observe exoplanetary transits; and importantly, projects such as the ETD, ExoClock (Kokori et al 2021(Kokori et al , 2022, and Exoplanet Watch (Zellem et al 2020) provide platforms that allow these observers to collectively contribute to cataloging light curves.…”

The Ariel Target List: The Impact of TESS and the Potential for Characterizing Multiple Planets within a System

“…Furthermore, the ephemerides of the potential planets must be well known to ensure efficient scheduling. Here again, work is underway to refine the periods of these worlds using citizen science, with thousands of light curves being observed by amateur facilities as part of the ExoClock project (Kokori et al 2021(Kokori et al , 2022 and by secondary-school students through the ORBYTS program (e.g., . Planets with nonlinear ephemerides, such as those within multiplanet systems that experience transit timing variations due to the gravitational interaction of the planets, will require particular care and attention (e.g., Dawson et al 2019;Kipping et al 2019;Ducrot et al 2020).…”