Signals of exomoons in averaged light curves of exoplanets

TL;DR

This paper introduces a novel method called Scatter Peak for directly detecting exomoons in transit light curves by analyzing local scatter, demonstrating promising results across various simulated data qualities and observational campaigns.

Contribution

The paper proposes the Scatter Peak method for exomoon detection, which is effective with around 100 transits and applicable to different data types, including ground-based and space-based observations.

Findings

Successful detection of 1 R_Earth moons around 1 R_Jupiter exoplanets in simulations

Detection limit of approximately 0.4 R_Earth for PLATO data

Method effective with ground-based and space-based data simulations

Abstract

The increasing number of transiting exoplanets sparked a significant interest in discovering their moons. Most of the methods in the literature utilize timing analysis of the raw light curves. Here we propose a new approach for the direct detection of a moon in the transit light curves via the so called Scatter Peak. The essence of the method is the valuation of the local scatter in the folded light curves of many transits. We test the ability of this method with different simulations: Kepler "short cadence", Kepler "long cadence", ground-based millimagnitude photometry with 3-min cadence, and the expected data quality of the planned ESA mission of PLATO. The method requires ~100 transit observations, therefore applicable for moons of 10-20 day period planets, assuming 3-4-5 year long observing campaigns with space observatories. The success rate for finding a 1 R_Earth moon around a 1 R_Jupiter exoplanet turned out to be quite promising even for the simulated ground-based observations, while the detection limit of the expected PLATO data is around 0.4 R_Earth. We give practical suggestions for observations and data reduction to improve the chance of such a detection: (i) transit observations must include out-of-transit phases before and after a transit, spanning at least the same duration as the transit itself; (ii) any trend filtering must be done in such a way that the preceding and following out-of-transit phases remain unaffected.