The Strongest Magnetic Fields on the Coolest Brown Dwarfs

Kao, Melodie M.; Hallinan, Gregg; Pineda, J. Sebastian; Stevenson, D. J.; Burgasser, Adam J.

doi:10.3847/1538-4365/aac2d5

Cited by 83 publications

(122 citation statements)

References 138 publications

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“…Ultracool dwarfs are also known to exhibit auroral activity (e.g. Kao et al 2018), which may account for observed Hα emission in these systems. It is expected that the transition from predominantly chromospheric to auroral Hα emission occurs during the L spectral type (Pineda et al 2017).…”

Section: Magnetic Activity Of L Dwarfsmentioning

confidence: 99%

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Detection of a giant white-light flare on an L2.5 dwarf with the Next Generation Transit Survey

Jackman

Wheatley

Burleigh

et al. 2019

Monthly Notices of the Royal Astronomical Society: Letters

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We present the detection of a ∆V ∼ -10 flare from the ultracool L2.5 dwarf ULAS J224940.13-011236.9 with the Next Generation Transit Survey (NGTS). The flare was detected in a targeted search of late-type stars in NGTS full-frame images and represents one of the largest flares ever observed from an ultracool dwarf. This flare also extends the detection of white-light flares to stars with temperatures below 2000 K. We calculate the energy of the flare to be 3.4 +0.9 −0.7 × 10 33 erg, making it an order of magnitude more energetic than the Carrington event on the Sun. Our data show how the high-cadence NGTS full-frame images can be used to probe white-light flaring behaviour in the latest spectral types.

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Section: Magnetic Activity Of L Dwarfsmentioning

confidence: 99%

“…Examples of this include periodic modulation due to clouds (e.g Gizis et al 2015), radio emission due to aurora in late L dwarfs (e.g. Kao et al 2018) and the presence of whitelight flares (e.g. Gizis et al 2013).…”

Section: Introductionmentioning

confidence: 99%

Detection of a giant white-light flare on an L2.5 dwarf with the Next Generation Transit Survey

Jackman

Wheatley

Burleigh

et al. 2019

Monthly Notices of the Royal Astronomical Society: Letters

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“…7in Birkby et al (2014), we estimate that transits would occur just 1 s earlier after 20 yr even if Q = 10 7 . Alternatively, magnetic effects such as magnetic breaking may force the system away from pseudo-synchronisation: magnetic fields are possessed by both BDs (of kG or stronger: Kao et al 2018;Berdyugina et al 2017;Metodieva et al 2017) and F stars (e.g. Mathur et al 2014;Augustson et al 2013).…”

Section: Tidal Evolution Of the Systemmentioning

confidence: 99%

Greening of the brown-dwarf desert

Persson

Csizmadia

Mustill

et al. 2019

A&A

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Context. Although more than 2000 brown dwarfs have been detected to date, mainly from direct imaging, their characterisation is difficult due to their faintness and model-dependent results. In the case of transiting brown dwarfs, however, it is possible to make direct high-precision observations. Aims. Our aim is to investigate the nature and formation of brown dwarfs by adding a new well-characterised object, in terms of its mass, radius and bulk density, to the currently small sample of less than 20 transiting brown dwarfs. Methods. One brown dwarf candidate was found by the KESPRINT consortium when searching for exoplanets in the K2 space mission Campaign 16 field. We combined the K2 photometric data with a series of multicolour photometric observations, imaging, and radial velocity measurements to rule out false positive scenarios and to determine the fundamental properties of the system. Results. We report the discovery and characterisation of a transiting brown dwarf in a 5.17-day eccentric orbit around the slightly evolved F7 V star EPIC 212036875. We find a stellar mass of 1.15 ± 0.08 M⊙, a stellar radius of 1.41 ± 0.05 R⊙, and an age of 5.1 ± 0.9 Gyr. The mass and radius of the companion brown dwarf are 51 ± 2 MJ and 0.83 ± 0.03 RJ, respectively, corresponding to a mean density of 108−13+15 g cm−3. Conclusions. EPIC 212036875 b is a rare object that resides in the brown-dwarf desert. In the mass-density diagram for planets, brown dwarfs, and stars, we find that all giant planets and brown dwarfs follow the same trend from ~0.3 MJ to the turn-over to hydrogen burning stars at ~ 73 MJ. EPIC 212036875 b falls close to the theoretical model for mature H/He dominated objects in this diagram as determined by interior structure models. We argue that EPIC 212036875 b formed via gravitational disc instabilities in the outer part of the disc, followed by a quick migration. Orbital tidal circularisation may have started early in its history for a brief period when the brown dwarf’s radius was larger. The lack of spin–orbit synchronisation points to a weak stellar dissipation parameter (Q⋆′ ≳ 108), which implies a circularisation timescale of ≳23 Gyr, or suggests an interaction between the magnetic and tidal forces of the star and the brown dwarf.

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“…and radio emission (Berger et al 2001;Berger 2002;Burgasser & Putman 2005;Berger 2006;Hallinan et al 2006Hallinan et al , 2007Hallinan et al , 2008Antonova et al 2007;Phan-Bao et al 2007;McLean et al 2011;McLean, Berger & Reiners 2012;Burgasser et al 2013;Williams, Cook & Berger 2014;Burgasser et al 2015;Kao et al 2016Kao et al , 2018Route & Wolszczan 2016a;Williams, Gizis & Berger 2017;) down to spectral type T6.5. In fact, Zeeman broadening and Zeeman Doppler imaging studies confirm surface-averaged magnetic field magnitudes of order kilogauss on dwarfs as late as M9 (Saar 1994;Johns-Krull & Valenti 1996;Donati et al 2006;Reiners & Basri 2007Morin et al 2010;Shulyak et al 2017), and pulsed radio emission associated with ∼kG fields has been observed on objects as late as T6.5 (Route & Wolszczan 2012;Kao et al 2016;Route & Wolszczan 2016a).…”

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confidence: 98%

Constraints on magnetospheric radio emission from Y dwarfs

Kao

Hallinan

Pineda

2019

Monthly Notices of the Royal Astronomical Society

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As a pilot study of magnetism in Y dwarfs, we have observed the three known infrared variable Y dwarfs WISE J085510.83−071442.5, WISE J140518.40+553421.4, and WISEP J173835.53+273258.9 with the NSF’s Karl G. Jansky Very Large Array in the 4–8 GHz frequency range. The aim was to investigate the presence of non-bursting quiescent radio emission as a proxy for highly circularly polarized radio emission associated with large-scale auroral currents. Measurements of magnetic fields on Y dwarfs may be possible by observing auroral radio emission, and such measurements are essential for constraining fully convective magnetic dynamo models. We do not detect any pulsed or quiescent radio emission, down to rms noise levels of 7.2 µJy for WISE J085510.83−071442.5, 2.2 µJy for WISE J140518.40+553421.4, and 3.2 µJy for WISEP J173835.53+273258.9. The fractional detection rate of radio emission from T dwarfs is ∼10 per cent suggesting that a much larger sample of deep observations of Y dwarfs is needed to rule out radio emission in the Y dwarf population. We discuss a framework that uses an empirical relationship between the auroral tracer Hα emission and quiescent radio emission to identify brown-dwarf auroral candidates. Finally, we discuss the implications that Y dwarf radio detections and non-detections can have for developing a picture of brown dwarf magnetism and auroral activity.

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The Strongest Magnetic Fields on the Coolest Brown Dwarfs

Cited by 83 publications

References 138 publications

Detection of a giant white-light flare on an L2.5 dwarf with the Next Generation Transit Survey

Detection of a giant white-light flare on an L2.5 dwarf with the Next Generation Transit Survey

Greening of the brown-dwarf desert

Constraints on magnetospheric radio emission from Y dwarfs

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