Global Analysis of the TRAPPIST Ultra-Cool Dwarf Transit Survey

TL;DR

This study reanalyzed data from the TRAPPIST survey to estimate the occurrence rate of close-in Earth-sized planets around ultra-cool dwarfs, demonstrating the pipeline's effectiveness in detecting such planets and suggesting a minimum 10% occurrence rate.

Contribution

It presents a fully automated pipeline for analyzing ultra-cool dwarf transit data and provides the first estimate of planet occurrence rates from the TRAPPIST survey.

Findings

Successfully detected TRAPPIST-1b and c transits without human intervention.

Achieved photometric precision sufficient to identify Earth-sized planets.

Estimated a minimum 10% occurrence rate of similar planets around ultra-cool dwarfs.

Abstract

We conducted a global analysis of the TRAPPIST Ultra-Cool Dwarf Transit Survey - a prototype of the SPECULOOS transit search conducted with the TRAPPIST-South robotic telescope in Chile from 2011 to 2017 - to estimate the occurrence rate of close-in planets such as TRAPPIST-1b orbiting ultra-cool dwarfs. For this purpose, the photometric data of 40 nearby ultra-cool dwarfs were reanalysed in a self-consistent and fully automated manner starting from the raw images. The pipeline developed specifically for this task generates differential light curves, removes non-planetary photometric features and stellar variability, and searches for transits. It identifies the transits of TRAPPIST-1b and TRAPPIST-1c without any human intervention. To test the pipeline and the potential output of similar surveys, we injected planetary transits into the light curves on a star-by-star basis and tested whether the pipeline is able to detect them. The achieved photometric precision enables us to identify Earth-sized planets orbiting ultra-cool dwarfs as validated by the injection tests. Our planet-injection simulation further suggests a lower limit of 10 per cent on the occurrence rate of planets similar to TRAPPIST-1b with a radius between 1 and 1.3 $R_\oplus$ and the orbital period between 1.4 and 1.8 days.