# Homogeneously derived transit timings for 17 exoplanets and reassessed TTV trends for WASP-12 and WASP-4

## TL;DR

This study homogeneously analyzed over 300,000 photometric measurements from 17 exoplanets spanning 16 years, confirming TTV trends in WASP-12 and reassessing trends in WASP-4 with implications for unseen companions and light-travel effects.

## Contribution

It provides a comprehensive, uniform analysis of transit timings for 17 exoplanets, incorporating new data and methods to clarify TTV trends and potential causes.

## Key findings

- Confirmed nonlinear TTV trend in WASP-12 with high significance.
- Detected hints of radial acceleration suggesting unseen distant companions.
- Reassessed TTV trend in WASP-4 as controversial and model-dependent.

## Abstract

We homogeneously analyse $\sim 3.2\times 10^5$ photometric measurements for $\sim 1100$ transit lightcurves belonging to $17$ exoplanet hosts. The photometric data cover $16$ years 2004--2019 and include amateur and professional observations. Old archival lightcurves were reprocessed using up-to-date exoplanetary parameters and empirically debiased limb-darkening models. We also derive self-consistent transit and radial-velocity fits for $13$ targets. We confirm the nonlinear TTV trend in the WASP-12 data at a high significance, and with a consistent magnitude. However, Doppler data reveal hints of a radial acceleration about $(-7.5\pm 2.2)$~m/s/yr, indicating the presence of unseen distant companions, and suggesting that roughly $10$ per cent of the observed TTV was induced via the light-travel (or Roemer) effect. For WASP-4, a similar TTV trend suspected after the recent TESS observations appears controversial and model-dependent. It is not supported by our homogeneus TTV sample, including $10$ ground-based EXPANSION lightcurves obtained in 2018 simultaneously with TESS. Even if the TTV trend itself does exist in WASP-4, its magnitude and tidal nature are uncertain. Doppler data cannot entirely rule out the Roemer effect induced by possible distant companions.