Characterizing Systemic Proper Motion Effects on Transiting Exoplanet Systems

Secular changes in exoplanet orbits are detectable in observations that span multiple decades in time. Because some exoplanets are now being observed over such timescales, it is possible to use long-term transit timing trends to investigate a wide range of dynamical interactions in planetary orbits, including those between planets and their host stars. The detected orbital decay of WASP-12 b is one example of these interactions. However, there are multiple effects, including systemic proper motion, that can cause apparent timing trends. Those trends can mask or enhance real orbital variations, and must be characterized before the true rate of secular evolution among exoplanets can be measured, revealing the rich dynamics of exoplanets or even probing their interiors. In this talk, we present our work on leveraging precise astrometric measurements from the Gaia Data Release 3 (DR3) catalogue to analyze the expected magnitudes of transit timing and duration variations for thousands of exoplanets, all due to systemic proper motion. Moreover, we compare the results for a subset of the exoplanetary systems to the expected magnitudes of long-term trends that are driven by physical phenomena, such as gravitational tides, perturbations from companion planets, rotational flattening, and general relativistic effects. We find that, in many cases, trends induced by systemic proper motion are measurable on decade timescales and may dominate secular signatures, particularly in the case of transit durations. We will outline the potential implications of this for the ongoing refinement of ephemerides and orbital evolution studies, as well as highlight systems of particular interest. We will also discuss how proper motion measurements may be seen as both a tool for establishing systematic uncertainty in observing physical effects and as means of constraining the 3D spatial orientation of the orbit. Our database serves as a practical tool for aiding the long-term monitoring of orbits, as the effects of proper motion will become increasingly important as measurement precision improves and observational baselines expand.