# Time-Resolved High Spectral Resolution Observation of 2MASSW J0746425+200032AB

## TL;DR

This study presents high spectral resolution, time-resolved observations of the brown dwarf binary 2MASSW J0746425+200032AB, finding no significant spectral variability and providing constraints on surface inhomogeneity.

## Contribution

It demonstrates the application of high spectral resolution monitoring to study brown dwarf surface features, setting new limits on spot coverage and variability.

## Key findings

- No coherent spectral variability modulated with rotation.
- Spot coverage smaller than 1% or 6.25% depending on contrast.
- Future observations can improve constraints on surface inhomogeneity.

## Abstract

Many brown dwarfs exhibit photometric variability at levels from tenths to tens of percents. The photometric variability is related to magnetic activity or patchy cloud coverage, characteristic of brown dwarfs near the L-T transition. Time-resolved spectral monitoring of brown dwarfs provides diagnostics of cloud distribution and condensate properties. However, current time-resolved spectral studies of brown dwarfs are limited to low spectral resolution (R$\sim$100) with the exception of the study of Luhman 16 AB at resolution of 100,000 using the VLT$+$CRIRES. This work yielded the first map of brown dwarf surface inhomogeneity, highlighting the importance and unique contribution of high spectral resolution observations. Here, we report on the time-resolved high spectral resolution observations of a nearby brown dwarf binary, 2MASSW J0746425+200032AB. We find no coherent spectral variability that is modulated with rotation. Based on simulations we conclude that the coverage of a single spot on 2MASSW J0746425+200032AB is smaller than 1\% or 6.25\% if spot contrast is 50\% or 80\% of its surrounding flux, respectively. Future high spectral resolution observations aided by adaptive optics systems can put tighter constraints on the spectral variability of 2MASSW J0746425+200032AB and other nearby brown dwarfs.