PACOME: Optimal multi-epoch combination of direct imaging observations for joint exoplanet detection and orbit estimation

TL;DR

PACOME is a novel algorithm that combines multi-epoch direct imaging observations by modeling orbital motion, significantly improving exoplanet detection sensitivity and enabling detection of previously undetectable sources.

Contribution

It introduces a multi-epoch combination framework that accounts for orbital motion, extending the PACO algorithm for enhanced exoplanet detection in direct imaging data.

Findings

PACOME detects synthetic exoplanets undetectable in mono-epoch analyses.

Detection sensitivity increases proportionally to the square root of the number of epochs.

It successfully detects known exoplanets in HR 8799 with high signal-to-noise ratios.

Abstract

Exoplanet detections and characterizations via direct imaging require high contrast and high angular resolution. These requirements typically require (i) cutting-edge instrumental facilities, (ii) optimized differential imaging to introduce a diversity in the signals of the sought-for objects, and (iii) dedicated processing algorithms to further eliminate the residual stellar leakages. Substantial efforts have been undertaken on the design of more efficient post-processing algorithms but their performance remains upper-bounded at shorter angular separations due to the the lack of diversity induced by the processing of each epoch of observations individually. We propose a new algorithm that is able to combine several observations of the same star by accounting for the Keplerian orbital motion across epochs of the sought-for sources in order to constructively co-add their weak signals. The proposed algorithm, PACOME, integrates an exploration of the plausible orbits within a statistical detection and estimation formalism. It is extended to a multi-epoch combination of the maximum likelihood framework of PACO, which is a mono-epoch post-processing algorithm. We derive a reliable multi-epoch detection criterion, interpretable both in terms of probability of detection and of false alarm. We tested the proposed algorithm on several datasets obtained from the VLT/SPHERE instrument with IRDIS and IFS. By resorting to injections of synthetic exoplanets, we show that PACOME is able to detect sources remaining undetectable in mono-epoch frameworks. The gain in detection sensitivity scales as high as the square root of the number of epochs. We also applied PACOME on a set of observations from the HR 8799 star hosting four known exoplanets, which are detected with very high signal-to-noise ratios. In addition, its implementation is efficient, fast, and fully automatized.