Searching for I band variability in stars in the M/L spectral transition region

TL;DR

This study conducted I band photometric observations of 21 late-type stars to identify variability, discovering four significantly variable sources and suggesting that variability is common among such stars, with no flares detected.

Contribution

First-time detection of variability in three brown dwarfs and comprehensive analysis of I band variability in M/L transition stars.

Findings

4 sources significantly variable at least once

29% of sources show variability including marginal cases

No flares detected from any source

Abstract

We report on I band photometric observations of 21 stars with spectral types between M8 and L4 made using the Isaac Newton Telescope. The total amount of time for observations which had a cadence of <2.3 mins was 58.5 hrs, with additional data with lower cadence. We test for photometric variability using the Kruskal-Wallis H-test and find that 4 sources (2MASS J10224821+5825453, 2MASS J07464256+2000321, 2MASS J16262034+3925190 and 2MASS J12464678+4027150) were found to be significantly variable at least on one epoch. Three of these sources are reported as photometrically variable for the first time. If we include sources which were deemed marginally variable, the number of variable sources is 6 (29 percent). No flares were detected from any source. The percentage of sources which we found were variable is similar to previous studies. We summarise the mechanisms which have been put forward to explain the light curves of brown dwarfs.