# A new take on the low-mass brown dwarf companions on wide-orbits in Upper-Scorpius

**Authors:** Simon Petrus, Mickaël Bonnefoy, Gaël Chauvin, Carine Babusiaux, Philippe Delorme, Anne-Marie Lagrange, Nathan Florent, Amelia Bayo, Markus Janson, Beth Biller, Elena Manjavacas, Gabriel-Dominique Marleau, Taisiya G. Kopytova  
**arXiv:** [1910.00347](https://arxiv.org/abs/1910.00347)  
**Date:** 2019-10-01  
**Summary page:** https://www.summarizepaper.com/en/paper/1910.00347v1/

## Key points

- The Upper-Scorpius association is a unique population of low-mass brown dwarfs
- Study aims to characterize the chemical and physical properties of three young, late-M brown-dwarfs claimed to be companions of the Upper Scorpius stars
- Spectra of six free floating analogues from the same association are analyzed for comparison
- Emission lines at UV and optical wavelengths are analyzed to investigate the presence of ongoing accretion processes
- X-Shooter spectrograph at VLT is used to obtain spectra over the 0.3–2.5 μm range simultaneously
- Forward modeling with ForMoSA code (Nested Sampling Bayesian inference method in using BT–SETTL15 models) is performed to infer Teff, log(g), and radius of objects
- Results are compatible with physical parameters found for free floating analogues of the association and with evolutionary model predictions
- Non-reproducibilities of BT–SETTL15 models for late M brown dwarfs limit accuracy on Teff estimates.
- Emission lines in several objects' spectra attributed to chromospheric activity except for USco1608–2315 which indicates active accretion.
- USco161031.9–16191305B is x4 over luminous; it could be explained by object activity if its companion is an unresolved multiple system.
- Study provides new insights into the physical and chemical properties of low mass brown dwarfs in the Upper Scorpius association and their potential mechanisms of formation.

## Summary

The Upper-Scorpius association is a unique population of low-mass (M<30 MJup) brown-dwarfs which offers an opportunity to explore their origin and mechanisms of formation. In this study, the authors aim to characterize the chemical and physical properties of three young, late-M brown-dwarfs claimed to be companions of the Upper Scorpius stars USco161031.9–16191305, HIP77900 and HIP78530 using medium resolution spectroscopy at UV (R~3300), optical (R~5400) and near infrared (R~4300) wavelengths. The spectra of six free floating analogues from the same association are analyzed for comparison and to explore potential physical differences between these substellar objects. The authors also analyze emission lines at UV and optical wavelengths to investigate the presence of ongoing accretion processes. They use the X–Shooter spectrograph at VLT to obtain the spectra of their targets over the 0.3–2.5 μm range simultaneously. By performing a forward modeling of the observed spectra with the ForMoSA code (Nested Sampling Bayesian inference method in using BT–SETTL15 models), they infer the Teff, log(g), and radius of their objects. The results are compatible with physical parameters found for free floating analogues of the association and with evolutionary model predictions. However, non–reproducibilities of BT–SETTL15 models for late M brown dwarfs limit accuracy on Teff estimates. The authors identify emission lines in several objects' spectra attributed to chromospheric activity except for USco1608–2315 for which they are indicative of active accretion. They confirm that USco161031.9–16191305B is x4 over luminous; it could be explained by object activity if its companion is an unresolved multiple system. Overall, this study provides new insights into the physical and chemical properties of low mass brown dwarfs in the Upper Scorpius association and their potential mechanisms of formation.