A Simplified Photodynamical Model for Planetary Mass Determination in Low-Eccentricity Multi-Transiting Systems

TL;DR

This paper introduces a fast, simplified photodynamical model to accurately determine planetary masses in low-eccentricity multi-planet systems using transit timing variations, validated on Kepler data.

Contribution

The authors develop and validate a new, efficient photodynamical modeling tool for planetary mass estimation from TTVs, improving accuracy and applicability to small exoplanets.

Findings

Validated model on Kepler-36, matching literature masses.

Improved mass estimates for Kepler-79 planets.

Provided first mass constraints for Kepler-450 and Kepler-595.

Abstract

Inferring planetary parameters from transit timing variations is challenging for small exoplanets because their transits may be so weak that determination of individual transit timing is difficult or impossible. We implement a useful combination of tools which together provide a numerically fast global photodynamical model. This is used to fit the TTV-bearing light-curve, in order to constrain the masses of transiting exoplanets in low eccentricity, multi-planet systems - and small planets in particular. We present inferred dynamical masses and orbital eccentricities in four multi-planet systems from Kepler's complete long-cadence data set. We test our model against Kepler-36 / KOI-277, a system with some of the most precisely determined planetary masses through TTV inversion methods, and find masses of 5.56 +0.41 -0.45 and 9.76 +0.79 -0.89 m_earth for Kepler-36 b and c, respectively - consistent with literature in both value and error. We then improve the mass determination of the four planets in Kepler-79 / KOI-152, where literature values were physically problematic to 12.5 +4.5 -3.6, 9.5 +2.3 -2:1, 11.3 +2.2 -2.2 and 6.3 +1.0 -1.0 m_earth for Kepler-79 b, c, d and e, respectively. We provide new mass constraints where none existed before for two systems. These are 12.5 +3.2 -2.6 m_earth for Kepler-450 c, and 3.3 +1.7 -1.0 and 17.4 +7.1 -3.8 m_earth for Kepler-595 c (previously KOI-547.03) and b, respectively. The photodynamical code used here, called PyDynamicaLC, is made publicly available.