The TROY project: Searching for co-orbital bodies to known planets

Abstract

Context. The detection of Earth-like planets, exocomets or Kuiper belts show that the different components found in the solar system should also be present in other planetary systems. Trojans are one of these components and can be considered fossils of the first stages in the life of planetary systems. Their detection in extrasolar systems would open a new scientific window to investigate formation and migration processes. Aims. In this context, the main goal of the TROY project is to detect exotrojans for the first time and to measure their occurrence rate (η-Trojan). In this first paper, we describe the goals and methodology of the project. Additionally, we used archival radial velocity data of 46 planetary systems to place upper limits on the mass of possible trojans and investigate the presence of co-orbital planets down to several tens of Earth masses. Methods. We used archival radial velocity data of 46 close-in (P < 5 days) transiting planets (without detected companions) with information from high-precision radial velocity instruments. We took advantage of the time of mid-transit and secondary eclipses (when available) to constrain the possible presence of additional objects co-orbiting the star along with the planet. This, together with a good phase coverage, breaks the degeneracy between a trojan planet signature and signals coming from additional planets or underestimated eccentricity. Results. We identify nine systems for which the archival data provide >1σ evidence for a mass imbalance between L4 and L5. Two of these systems provide >2σ detection, but no significant detection is found among our sample. We also report upper limits to the masses at L4/L5 in all studied systems and discuss the results in the context of previous findings.

Understanding WASP-12b

“…We estimate that a roughly lunar mass in a "horseshoe" 1:1 resonant libration could modulate WASP 12b's period at this amplitude. This would easily satisfy the limit m c < 34 M on Trojan companions to WASP-12b found by Lillo-Box et al (2018), who based their analysis on archival radial velocities. The difficulty, however, is in the period of the modulation.…”

Ploonets: formation, evolution, and detectability of tidally detached exomoons

“…Several authors (see e.g. Nesvorný 2009;Vokrouhlický & Nesvorný 2014;Lillo-Box et al 2018 and references therein) have already studied the problem of the stability and detection by TTVs of sub planetary coorbital companions in extrasolar systems. In this work, we adopted the prescription suggested in the guide of the Nbody simulator REBOUND (Rein & Liu 2012).…”

The TROY project

“…We used the archive radial velocity data presented in Lillo-Box et al (2018a) and newly acquired high-resolution spectra from HARPS (Mayor et al 2003), HARPS-N (Cosentino et al 2012), and CARMENES (Quirrenbach et al 2014). In Table 1 we present a summary of the new radial velocity observations obtained for each of the nine systems, distinguishing between archive and new observations.…”

“…Some of the systems studied in Lillo-Box et al (2018a) showed hints of a mass imbalance between the two Lagrangian points at the 2σ level. Even though they were not significant detections, they certainly deserve additional follow up.…”