The TROY project III. Exploring co-orbitals around low-mass stars (2407.04677v1)

Abstract: Co-orbital objects, also known as trojans, are frequently found in simulations of planetary system formation. In these configurations, a planet shares its orbit with other massive bodies. It is still unclear why there have not been any co-orbitals discovered thus far in exoplanetary systems or even pairs of planets found in such a 1:1 mean motion resonance. Reconciling observations and theory is an open subject in the field. The main objective of the TROY project is to conduct an exhaustive search for exotrojans using diverse observational techniques. In this work, we analyze the radial velocity time series informed by transits, focusing the search around low-mass stars. We employed the alpha-test method on confirmed planets searching for shifts between spectral and photometric mid-transit times. This technique is sensitive to mass imbalances within the planetary orbit, allowing us to identify non-negligible co-orbital masses. Among the 95 transiting planets examined, we find one robust exotrojan candidate with a significant 3-sigma detection. Additionally, 25 exoplanets show compatibility with the presence of exotrojan companions at a 1-sigma level, requiring further observations to better constrain their presence. For two of those weak candidates, we find dimmings in their light curves within the predicted Lagrangian region. We established upper limits on the co-orbital masses for either the candidates and null detections. Our analysis reveals that current high-resolution spectrographs effectively rule out co-orbitals more massive than Saturn around low-mass stars. This work points out to dozens of targets that have the potential to better constraint their exotrojan upper mass limit with dedicated radial velocity observations. We also explored the potential of observing the secondary eclipses of the confirmed exoplanets to enhance the exotrojan search.

• The paper investigates co-orbital configurations (exotrojans) around 95 transiting exoplanets orbiting low-mass stars using radial velocity data and the $\alpha$-test method.
• Analysis identified one strong exotrojan candidate and found that co-orbitals exceeding Saturn's mass are unlikely around low-mass stars based on current detection limits.
• The findings refine search parameters for future observational campaigns and highlight the need for continued radial velocity monitoring to confirm exotrojan existence.

Analysis of Co-orbital Phenomena in Exoplanetary Systems Around Low-Mass Stars

This paper comprehensively explores co-orbital configurations, specifically referred to as exotrojans, in planetary systems orbiting low-mass stars. Known as co-orbitals, these planetary arrangements involve a primary planet sharing its orbit with one or more significant bodies. Despite their common occurrence in simulations, their empirical detection in exoplanetary systems remains elusive. This investigation, forming part of the T project series, aims to reconcile theoretical predictions with observed phenomena through rigorous analysis of radial velocity (RV) data, targeting primarily low-mass stars.

Methodology and Findings

The observational strategy is grounded in analyzing shifts in mid-transit times derived from RV observations, using the $\alpha$-test method. This approach enables the detection of non-negligible mass distribution disparities within the orbit under examination. Among 95 studied transiting exoplanets, the research identified one strong exotrojan candidate with a 3-$\sigma$ detection significance. Further, 25 exoplanets exhibit potential exotrojan presence at a 1-$\sigma$ threshold, suggesting these require more detailed follow-up observations.

Upper limits on potential co-orbital masses were a core aspect of the analysis, revealing that current technological capabilities straightforwardly negate the existence of co-orbitals exceeding Saturn's mass around low-mass stars. This vital insight refines the search parameters for potential exotrojan systems, steering observational efforts toward more promising candidates.

Implications and Future Directions

The indications from this paper open various avenues for future research and provide essential baselines for the frequency estimation of exotrojan bodies. Practically, this work advises targeted RV monitoring strategies and suggests that including secondary eclipse observations can significantly enhance detection accuracy. Additionally, advances in ground-based and space-based spectrograph capabilities may offer deeper insights into exotrojan systems, improving detection fidelity.

Conclusion

This research serves as a substantial contribution toward understanding the prevalence and characteristics of exotrojan systems. By narrowing the parameter space for possible co-orbital configurations, it refines the focus for subsequent observational campaigns. Crucially, it underscores the necessity for continued and dedicated RV observations to definitively ascertain the existence and properties of exotrojan systems. As instrumentation and analytical methods advance, the detection and characterization of such systems around low-mass stars will become increasingly feasible.