# The COBREX archival survey: improved constraints on the occurrence rate of wide-orbit substellar companions. I. A uniform re-analysis of 400 stars from the GPIES survey

**Authors:** V. Squicciarini, J. Mazoyer, A. -M. Lagrange, A. Chomez, P. Delorme, O. Flasseur, F. Kiefer  
**arXiv:** [2411.06157](https://arxiv.org/abs/2411.06157)  
**Date:** 2024-11-09  
**Summary page:** https://www.summarizepaper.com/en/paper/2411.06157v1/

## Key points

- Direct imaging campaigns are essential for exploring outer regions around young stars in search of giant exoplanet and brown dwarf companions.
- Advanced post-processing techniques have been developed to bridge the gap between radial velocity and direct imaging capabilities, enhancing detection performance without additional instrumental costs.
- The COBREX project focuses on re-analyzing data from 400 stars observed as part of the GPIES survey at GPI@Gemini South using the PACO algorithm.
- Researchers were able to estimate unbiased occurrence frequencies of giant planets and brown dwarfs in the target region by converting detection limits into detectability maps.
- Significant improvements in detection limits were achieved, with up to a twofold increase in minimum detectable mass for potential substellar companions.

## Summary

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Direct imaging campaigns are essential for exploring the outer regions around young stars in search of giant exoplanet and brown dwarf companions. These campaigns provide crucial complementary information to radial velocity and transit searches, significantly contributing to demographic studies in the field of exoplanet research. However, the critical 5-20 au region, where most giant planets are believed to form, has remained poorly explored due to limitations between radial velocity and direct imaging capabilities. To bridge this gap, advanced post-processing techniques have been developed to enhance detection performance without additional instrumental costs. The COBREX project is a significant effort in this direction, assembling the largest collection of archival direct imaging observations for a large-scale uniform re-analysis. This paper focuses on re-analyzing data from 400 stars observed as part of the GPIES survey conducted at GPI@Gemini South. The re-analysis process involved pre-reduction of raw frames followed by processing data cubes using the PACO algorithm. Candidate detections were identified and vetted through multi-epoch proper motion analysis and examination of color-magnitude diagrams. By converting detection limits into detectability maps, researchers were able to estimate unbiased occurrence frequencies of giant planets and brown dwarfs in the target region. Significant improvements in detection limits were achieved compared to previous studies, with up to a twofold increase in minimum detectable mass for potential substellar companions. While no new substellar companion was confirmed during this study, two intriguing planet candidates were identified for further follow-up observations. The findings from this re-analysis contribute valuable insights into the occurrence rate of wide-orbit substellar companions within specific mass and orbital range criteria. These derived occurrence rates provide important constraints for understanding the formation and distribution of giant planets and brown dwarfs in distant orbits around young stars. This comprehensive study underscores the potential of advanced post-processing techniques in maximizing the scientific output from existing direct imaging datasets, paving the way for future discoveries in exoplanet research.