The brown dwarf atmosphere monitoring (BAM) project

Abstract

Using the SofI instrument on the 3.5 m New Technology Telescope, we have conducted an extensive near-infrared monitoring survey of an unbiased sample of 69 brown dwarfs spanning the L0 to T8 spectral range, with at least one example of each spectral type. Each target was observed for a 2−4 h period in the J s -band, and the median photometric precision of the data is ∼0.7%. A total of 14 brown dwarfs were identified as variables with min-to-max amplitudes ranging from 1.7% to 10.8% over the observed duration. All variables satisfy a statistical significance threshold with a p-value ≤5% based on comparison with a median reference star light curve. Approximately half of the variables show pure sinusoidal amplitude variations similar to 2MASSJ2139+0220, and the remainder show multi-component variability in their light curves similar to SIMPJ0136+0933. It has been suggested that the L-T transition should be a region of a higher degree of variability if patchy clouds are present, and this survey was designed to test the patchy cloud model with photometric monitoring of both the L-T transition and non-transition brown dwarfs. The measured frequency of variables is 13 +10 −4 % across the L7−T4 spectral range, indistinguishable from the frequency of variables of the earlier spectral types (30 +11 −8 %), the later spectral types (13 +10 −4 %), or the combination of all non-transition region brown dwarfs (22 +7 −5 %). The variables are not concentrated in the transition, in a specific colour, or in binary systems. Of the brown dwarfs previously monitored for variability, only ∼60% maintained the state of variability (variable or constant), with the remaining switching states. The 14 variables include 9 newly identified variables that will provide important systems for follow-up multi-wavelength monitoring to further investigate brown dwarf atmosphere physics.

Spectral Variability of Two Rapidly Rotating Brown Dwarfs: 2MASS J08354256-0819237 and 2MASS J18212815+1414010

“…There is no Li I absorption reported for this source (Cruz et al 2003;Burgasser et al 2015); however its low temperature (T ef f =1800 K Gagné et al 2015) and likely youth (<1 Gyr) is consistent with a mass below the hydrogen-burning mass limit (Baraffe et al 2003;Burrows et al 2000). This source has been reported to vary in both optical and near-infrared bands with a period of 3.1 hr and an amplitude of ∼1% (Koen 2004;Wilson et al 2014). Its v sin i = 14.2±0.4 km s −1 (Blake et al 2010) suggests a near pole-on viewing angle assuming a radius 2 R = 1 R Jup .…”

Doppler imaging of exoplanets and brown dwarfs

“…These are taken from SIMBAD and the work of Konopacky et al (2010), Luhman (2013), Martín et al (1999), McCaughrean et al (2004), Probst (1983), Reid et al (2000), Reid et al (2001), Scholz (2010), White (1999), Wilson et al (2014), and Zapatero …”

The brown dwarf atmosphere monitoring (BAM) project – II. Multi-epoch monitoring of extremely cool brown dwarfs

“…To place the BAM-II results in the broader context of the brown dwarf population, Figure 5 combines the targets in both this study, and the previous BAM-I survey spanning the full L0-T8 sequence (Wilson, Rajan & Patience 2014). Single epoch BAM-I variables are also included in the comparison.…”

“…Over the past several years, we have conducted a largescale photometric variability survey of brown dwarfs -the Brown dwarf Atmosphere Monitoring (BAM) program. The initial BAM study (Wilson, Rajan & Patience 2014) covered 69 targets spanning the L0-T8 sequence, and detected multiple late-T variables. In this paper, we present the results of the second component of the BAM project that is designed to search for photometric variability over several epochs in four ultracool brown dwarfs at or near the T/Y spectral boundary.…”