# Exploring the Extremes: Characterizing a New Population of Old and Cold Brown Dwarfs

**Authors:** A. M. Meisner, S. K. Leggett, S. E. Logsdon, A. C. Schneider, P. Tremblin, M. Phillips  
**arXiv:** [2301.09817](https://arxiv.org/abs/2301.09817)  
**Date:** 2023-01-24  
**Summary page:** https://www.summarizepaper.com/en/paper/2301.09817v1/

## Key points

- A new population of old and cold brown dwarfs has been characterized in a recent study.
- This population is important for understanding the metallicity dependence of low-temperature atmospheres and the substellar mass function.
- The newly discovered population includes extreme T-type subdwarfs and possibly the first Y-type subdwarf, WISEA J153429.75$-$104303.3.
- Researchers conducted a Gemini YJHK/Ks photometric follow-up campaign to investigate this population further.
- They present 14 near-infrared photometric detections of 8 unique targets: six T subdwarf candidates, one moderately metal poor Y dwarf candidate, and one Y subdwarf candidate.
- The team obtained the first-ever ground-based detection of WISEA J153429.75$-$104303.3, an object with highly anomalous properties compared to other late-T and Y dwarfs.
- The F110W$-$J color of WISEA J153429.75$-$104303.3 is significantly bluer than that of other objects in its class, indicating an unusual spectrum in the 0.9–1.4 $\mu$m wavelength range that encompasses the $J$-band peak.

## Summary

In a recent study, A. M. Meisner and colleagues have characterized a new population of old and cold brown dwarfs, which is crucial for understanding the metallicity dependence of low-temperature atmospheres and the substellar mass function. This newly discovered population includes what may be the first known "extreme T-type subdwarfs" and possibly the first Y-type subdwarf, WISEA J153429.75$-$104303.3. To further investigate this population, the researchers conducted a Gemini YJHK/Ks photometric follow-up campaign targeting potentially metal-poor T and Y dwarfs using GNIRS and Flamingos-2 instruments. They present 14 near-infrared photometric detections of 8 unique targets: six T subdwarf candidates, one moderately metal poor Y dwarf candidate, and one Y subdwarf candidate. The team obtained the first-ever ground-based detection of WISEA J153429.75$-$104303.3, an object with highly anomalous properties compared to other late-T and Y dwarfs. The F110W$-$J color of WISEA J153429.75$-$104303.3 is significantly bluer than that of other objects in its class, indicating an unusual spectrum in the 0.9–1.4 $\mu$m wavelength range that encompasses the $J$-band peak.