# JWST/NIRCam discovery of the first Y+Y brown dwarf binary: WISE J033605.05$-$014350.4

**Authors:** Per Calissendorff, Matthew De Furio, Michael Meyer, Loïc Albert, Christian Aganze, Mohamad Ali-Dib, Daniella C. Bardalez Gagliuffi, Frederique Baron, Charles A. Beichman, Adam J. Burgasser, Michael C. Cushing, Jacqueline Kelly Faherty, Clémence Fontanive, Christopher R. Gelino, John E. Gizis, Alexandra Z. Greenbaum, J. Davy Kirkpatrick, Sandy K. Leggett, Frantz Martinache, David Mary  
**arXiv:** [2303.16923](https://arxiv.org/abs/2303.16923)  
**Date:** 2023-03-29  
**Summary page:** https://www.summarizepaper.com/en/paper/2303.16923v1/

## Key points

- Calissendorff et al. discovered the first brown dwarf binary system with a Y dwarf primary, WISE J033605.05$-$014350.4
- NIRCam on JWST with F150W and F480M filters were used to observe the system
- An empirical point spread function binary model was employed to identify the companion
- The companion is located at a projected separation of 84 milliarcseconds, position angle of 295 degrees, and has a contrast of 2.8 and 1.8 magnitudes in F150W and F480M, respectively
- The system is estimated to be at a distance of 10$\,$pc from Earth based on its Spitzer parallax
- The physical separation between the two objects is approximately 1$\,$au assuming a random inclination distribution
- Evolutionary models predict that for an age of 1-5 Gyr, the companion mass is about 4-12.5 Jupiter masses around the primary which has a mass between 7.5-20 Jupiter masses; this corresponds to a companion-to-host mass fraction of $q=0.61\pm0.05$
- Under the assumption of a Keplerian orbit, it is estimated that this extreme binary has a period in the range of 5-9 years
- This discovery joins a small but growing sample of ultracool dwarf binaries with effective temperatures of a few hundreds Kelvin which are important for understanding formation mechanisms for these elusive objects as they allow us to investigate whether companions formed as stars or as planets in disks around their primaries.
- An empirical PSF fitting routine using empirically derived PSF models based on Anderson & King's (2000) ePSF construction method was applied by Calissendorff et al to search for companions at small separations

## Summary

In a recent study, Calissendorff et al. report the discovery of the first brown dwarf binary system with a Y dwarf primary, WISE J033605.05$-$014350.4. The team used NIRCam on JWST with the F150W and F480M filters to observe the system and employed an empirical point spread function binary model to identify the companion. The companion is located at a projected separation of 84 milliarcseconds, position angle of 295 degrees, and has a contrast of 2.8 and 1.8 magnitudes in F150W and F480M, respectively. Based on its Spitzer parallax, the system is estimated to be at a distance of 10$\,$pc from Earth, and assuming a random inclination distribution, the physical separation between the two objects is approximately 1$\,$au. Evolutionary models predict that for an age of 1-5 Gyr, the companion mass is about 4-12.5 Jupiter masses around the primary which has a mass between 7.5-20 Jupiter masses; this corresponds to a companion-to-host mass fraction of $q=0.61\pm0.05$. Under the assumption of a Keplerian orbit, it is estimated that this extreme binary has a period in the range of 5-9 years. The discovery joins a small but growing sample of ultracool dwarf binaries with effective temperatures of a few hundreds Kelvin which are important for understanding formation mechanisms for these elusive objects as they allow us to investigate whether companions formed as stars or as planets in disks around their primaries. To search for companions at small separations, Calissendorff et al applied an empirical PSF fitting routine using empirically derived PSF models based on Anderson & King's (2000) ePSF construction method which has been previously used to find close companions on sub-pixel scales using Hubble Space Telescope images.