ExoClock Project IV: A homogeneous catalogue of 620 updated exoplanet ephemerides

TL;DR

ExoClock IV delivers a homogeneous catalogue of 620 updated exoplanet ephemerides by integrating ~30,000 mid-transit times from the ExoClock network, literature, and space-based missions Kepler, K2, and TESS. Using limb-darkening modeling, BJD_TDB time standardization, and MCMC ephemeris fitting, the work achieves a median 2029 prediction-uncertainty improvement of about $7.9$ times and the identification of TTVs across multiple systems. The data release (DRD) provides two products—Catalogue of Observations and Catalogue of ExoClock Ephemerides—open to the community, with stringent quality criteria ensuring reliable scheduling for Ariel and larger facilities. The study underscores the importance of continuous monitoring, synchronous multi-telescope campaigns, and collaboration with larger facilities to address the specific needs of bright, shallow-transit, or multi-planet targets, ultimately enhancing mission efficiency and scientific return.

Abstract

The ExoClock project is an open platform aiming to monitor exoplanets by integrating observations from space and ground based telescopes. This study presents an updated catalogue of 620 exoplanet ephemerides, integrating 30000 measurements from ground-based telescopes (the ExoClock network), literature, and space telescopes (Kepler, K2 and TESS). The updated catalogue includes 277 planets from TESS which require special observing strategies due to their shallow transits or bright host stars. This study demonstrates that data from larger telescopes and the employment of new methodologies such as synchronous observations with small telescopes, are capable of monitoring special cases of planets. The new ephemerides show that 45% of the planets required an update while the results show an improvement of one order of magnitude in prediction uncertainty. The collective analysis also enabled the identification of new planets showing TTVs, highlighting the importance of extensive observing coverage. Developed in the context of the ESA's Ariel space mission, with the goal of delivering a catalogue with reliable ephemerides to increase the mission efficiency, ExoClock's scope and service have grown well beyond the remit of Ariel. The ExoClock project has been operating in the framework of open science, and all tools and products are accessible to everyone within academia and beyond, to support efficient scheduling of future exoplanet observations, especially from larger telescopes where the pressure for time allocation efficiency is higher (Ariel, JWST, VLT, ELT, Subaru etc). The inclusion of diverse audiences in the process and the collaborative mode not only foster democratisation of science but also enhance the quality of the results.

Figures (7)

• Figure 1: Cumulative distribution of observations published by the ExoClock network.
• Figure 2: Distribution of transit mid-time uncertainties among the different sources.
• Figure 3: Distribution of coverage among the different sources. As coverage we define the percentage of years (since the first observation in the database) for which at least one observation exists.
• Figure 4: De-trended and binned observations for the 2022-06-14 synchronous campaign on HD191939b compared to a TESS observation acquired 1 orbit earlier. Binning has been performed only for visualisation purposes. The fitting has been performed on the original data, without binning.
• Figure 5: Comparison of the 2029-prediction uncertainties between this work and ExoClock III (left), or between this work and the ephemerides used when the planet was inserted to the ExoClock target list (right). With the red star we indicate the planets with a "TTVs" flag. In both panels, the dashed lines indicate no change ($\sigma_{p'}=\sigma_{p}$).