A search for short time-scale<i>JHK</i>variability in ultracool dwarfs

Koen, C.; Matsunaga, Noriko; Menzies, J.

doi:10.1111/j.1365-2966.2004.08208.x

Cited by 43 publications

(64 citation statements)

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“…Previous observations designed to search for photometric variability have been reported for approximately half the sample -34 targets -and cover optical (Gelino et al 2002;Koen 2013), near-IR (Enoch et al 2003;Koen et al 2004Koen et al , 2005Clarke et al 2008;Khandrika et al 2013;Buenzli et al 2014), and radio wavelengths. It is important to note that the different variability monitoring studies apply different criteria to categorise a target as variable or constant, and a range of observation wavelengths have been employed.…”

Section: The Bam Samplementioning

confidence: 99%

“…Several previous surveys have targeted smaller sample sets (e.g. Enoch et al 2003;Koen et al 2004Koen et al , 2005Clarke et al 2008;Khandrika et al 2013;Girardin et al 2013;Buenzli et al 2014) or searched in different wavelengths such as I-band (e.g. Gelino et al 2002;Koen 2004Koen , 2013.…”

Section: Comparison Of Variables With Previous Studiesmentioning

confidence: 99%

“…Artigau et al (2003) [A03]; Artigau et al (2009) [A09]; Apai et al (2013) [Ap13]; [B06]; Buenzli et al (2012) [Bu12]; Buenzli et al (2014) [Bu13]; Clarke et al (2008) [C08]; Enoch et al (2003) [E03]; Gelino et al (2002) [G02]; Khandrika et al (2013) [Kh13]; Koen (2004) [K04]; Koen et al (2004) [KMM04]; Koen et al (2005) [KTTK05]; Koen (2005) [K05]; Koen (2013) [K13]; Radigan et al (2012) [R12]; Zapatero Osorio et al (2006) [Z06].…”

Section: The Sensitivity Of the Bam Surveymentioning

confidence: 99%

“…2MASS J22282889-4310262 Clarke et al 2008;Buenzli et al 2012, SIMP J013656.5+093347.3 Artigau et al 2009, 2MASS J21392676+0220226 Radigan et al 2012, as well as objects recorded as variable in one wavelength range, but not another (e.g. 2MASS J15344984-2952274, Koen et al 2004). A small set of variable sources have been monitored contemporaneously at multiple wavelengths, with the combined results being used to infer the vertical extent of atmospheric features and to investigate atmospheric circulation patterns (e.g.…”

Section: Introductionmentioning

confidence: 99%

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The brown dwarf atmosphere monitoring (BAM) project

Wilson

Rajan

Patience

2014

A&A

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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.

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Section: The Bam Samplementioning

confidence: 99%

Section: Comparison Of Variables With Previous Studiesmentioning

confidence: 99%

Section: The Sensitivity Of the Bam Surveymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The brown dwarf atmosphere monitoring (BAM) project

Wilson

Rajan

Patience

2014

A&A

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“…At nearinfrared (NIR) wavelengths, which are sensitive to changes in cloud opacity, photometric monitoring of brown dwarfs has revealed low-level variability to be common across the entire L-T sequence (Koen et al 2004(Koen et al , 2005Clarke et al 2008;Radigan et al 2014). Extrapolations from space-based surveys suggest that most, if not all, brown dwarfs have patchy photospheres to some degree (Buenzli et al 2014;Metchev et al 2014).…”

Section: Introductionmentioning

confidence: 99%

An Independent Analysis of the Brown Dwarf Atmosphere Monitoring (Bam) Data: Large-Amplitude Variability Is Rare Outside the L/T Transition

Radigan

2014

ApJ

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Observations of variability can provide valuable information about the processes of cloud formation and dissipation in brown dwarf atmospheres. Here we report the results of an independent analysis of archival data from the Brown dwarf Atmosphere Monitoring (BAM) program. Time series data for 14 L and T dwarfs reported to be significantly variable over timescales of hours were analyzed. We confirm large-amplitude variability (amplitudes >2%) for 4 out of 13 targets and place upper limits of 0.7%-1.6% on variability in the remaining sample. For two targets we find evidence of weak variability at amplitudes of 1.3% and 1.6%. Based on our revised classification of variable objects in the BAM study, we find strong variability outside the L/T transition to be rare at near infrared wavelengths. From a combined sample of 81 L0-T9 dwarfs from the revised BAM sample and the variability survey of Radigan et al., we infer an overall observed frequency for large-amplitude variability outside the L/T transition of 3.2 +2.8 −1.8 %, in contrast to 24 +11 −9 % for L9-T3.5 spectral types. We conclude that while strong variability is not limited to the L/T transition, it occurs more frequently in this spectral type range, indicative of larger or more highly contrasting cloud features at these spectral types.

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Theoretical modelling of optical and IR spectra of brown dwarfs and ultracool dwarfs

Pavlenko¹

2005

Astron Nachr

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Abstract. The current state of theoretical modelling of the spectra of cool dwarfs and ultracool objects are discussed. Fits of synthetical spectral energy distributions (SEDs) in the optical and IR spectral regions to observed spectra show problems of theoretical modelling. Problems of interpretation of observed spectra are more obvious for the case of L and T dwarfs. Still even for late-M dwarfs the situation is far from being perfect. Some examples of the fine analysis of the spectra of ultracool dwarfs are presented.

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A search for short time-scaleJHKvariability in ultracool dwarfs

Cited by 43 publications

References 23 publications

The brown dwarf atmosphere monitoring (BAM) project

The brown dwarf atmosphere monitoring (BAM) project

An Independent Analysis of the Brown Dwarf Atmosphere Monitoring (Bam) Data: Large-Amplitude Variability Is Rare Outside the L/T Transition

Theoretical modelling of optical and IR spectra of brown dwarfs and ultracool dwarfs

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