# Detection of co-orbital planets by combining transit and radial-velocity measurements

## TL;DR

This paper proposes a new method combining transit and radial-velocity data to detect co-orbital planets, which are difficult to observe with traditional methods, by analyzing a parameter related to their mass ratio.

## Contribution

It introduces a simple, effective detection technique for co-orbital planets using a single parameter, applicable to eccentric orbits, enhancing observational capabilities.

## Key findings

- Method successfully identifies co-orbital candidates when parameter α differs from zero.
- Applicable to eccentric orbits, broadening detection scenarios.
- Discusses false positive scenarios to improve detection reliability.

## Abstract

Co-orbital planets have not yet been discovered, although they constitute a frequent by-product of planetary formation and evolution models. This lack may be due to observational biases, since the main detection methods are unable to spot co-orbital companions when they are small or near the Lagrangian equilibrium points. However, for a system with one known transiting planet (with mass $m_1$), we can detect a co-orbital companion (with mass $m_2$) by combining the time of mid-transit with the radial-velocity data of the star. Here, we propose a simple method that allows the detection of co-orbital companions, valid for eccentric orbits, that relies on a single parameter $\alpha$, which is proportional to the mass ratio $m_2/m_1$. Therefore, when $\alpha$ is statistically different from zero, we have a strong candidate to harbour a co-orbital companion. We also discuss the relevance of false positives generated by different planetary configurations.