Electron-Beam-Induced Radio Emission From Ultracool Dwarfs

Yu, Shenghua; Doyle, J. G.; Kuznetsov, A. A.; Hallinan, Gregg; Antonova, A.; MacKinnon, A. L.; Golden, Aaron

doi:10.1088/0004-637x/752/1/60

Cited by 14 publications

(14 citation statements)

References 57 publications

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“…For the L3.5 dwarf 2MASS J00361617+1821104, Hallinan et al (2008) showed that the radio emission is originally due to the ECM, but perhaps depolarized during propagation toward the observer. In addition, recent particle-in-cell numerical simulations by Yu et al (2012) have shown that, under certain circumstances, maser emission can be intrinsically weakly polarized. The same mechanism can be applied to generate the bright, 100% polarized burst/flare detected from another ultracool dwarf -DENIS-P J104814.9-395604 (Burgasser & Putman 2005).…”

Section: Radiation Mechanisms and Geometric Effectmentioning

confidence: 99%

Volume-limited radio survey of ultracool dwarfs

Antonova

Hallinan

Doyle³

et al. 2013

A&A

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Aims. We aim to increase the sample of ultracool dwarfs studied in the radio domain to allow a more statistically significant understanding of the physical conditions associated with these magnetically active objects. Methods. We conducted a volume-limited survey at 4.9 GHz of 32 nearby ultracool dwarfs with spectral types covering the range M7-T8. A statistical analysis was performed on the combined data from the present survey and previous radio observations of ultracool dwarfs. Results. Whilst no radio emission was detected from any of the targets, significant upper limits were placed on the radio luminosities that are below the luminosities of previously detected ultracool dwarfs. Combining our results with those from the literature gives a detection rate for dwarfs in the spectral range M7-L3.5 of ∼9%. In comparison, only one dwarf later than L3.5 is detected in 53 observations. We report the observed detection rate as a function of spectral type and the number distribution of the dwarfs as a function of spectral type and rotation velocity. Conclusions. The radio observations to date point to a drop in the detection rate toward the ultracool dwarfs. However, the emission levels of detected ultracool dwarfs are comparable to those of earlier type active M dwarfs, which may imply that a mildly relativistic electron beam or a strong magnetic field can exist in ultracool dwarfs. Fast rotation may be a sufficient condition to produce magnetic fields strengths of several hundred Gauss to several kilo Gauss, as suggested by the data for the active ultracool dwarfs with known rotation rates. A possible reason for the non-detection of radio emission from some dwarfs is that maybe the centrifugal acceleration mechanism in these dwarfs is weak (due to a low rotation rate) and thus cannot provide the necessary density and/or energy of accelerated electrons. An alternative explanation could be long-term variability, as is the case for several ultracool dwarfs whose radio emission varies considerably over long periods with emission levels dropping below the detection limit in some instances.

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Section: Radiation Mechanisms and Geometric Effectmentioning

confidence: 99%

Volume-limited radio survey of ultracool dwarfs

Antonova

Hallinan

Doyle³

et al. 2013

A&A

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“…To create the framework to model polarised bursts from UCDs, Yu et al (2012) simulated the micro-physics of the immediate environment around late type dwarfs. Other work, such as Kuznetsov et al (2012) and Hallinan et al (2015), have created models which take physically realistic environmental conditions coupled with different geometries for the magnetic field to simulate individual polarised radio bursts.…”

Section: Introductionmentioning

confidence: 99%

Modelling the environment around five ultracool dwarfs via the radio domain

Metodieva

Kuznetsov

Antonova

et al. 2016

Mon. Not. R. Astron. Soc.

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We present the results of a series of short radio observations of six ultracool dwarfs made using the upgraded VLA in S (2-4GHz) and C (4-7GHz) bands. LSR J1835+3259 exhibits a 100 percent right-hand circularly polarised burst which shows intense narrowband features with a fast negative frequency drift of about −30 MHz s −1 . They are superimposed on a fainter broadband emission feature with a total duration of about 20 minutes, bandwidth of about 1 GHz, centred at about 3.5 GHz, and a slow positive frequency drift of about 1 MHz s −1 . This makes it the first such event detected below 4 GHz and the first one exhibiting both positive and negative frequency drifts. Polarised radio emission is also seen in 2MASS J00361617+1821104 and NLTT 33370, while LP 349-25 and TVLM 513-46546 have unpolarised emission and BRI B0021-0214 was not detected. We can reproduce the main characteristics of the burst from LSR J1835+3259 using a model describing the magnetic field of the dwarf as a tilted dipole. We also analyse the origins of the quiescent radio emission and estimate the required parameters of the magnetic field and energetic electrons. Although our results are non-unique, we find a set of models which agree well with the observations.

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“…In practice, the ECMI occurs in regions that span a variety of field strengths, so the observed emission has a moderate bandwidth, ∆ν/ν ∼ 1 (Zarka et al 2001), with a cutoff at high frequencies because the body's magnetic field reaches some peak value at its surface. ECMI emission is beamed and likely refracts through the plasmasphere that evidently envelops the radio-active UCDs, necessitating detailed simulations to predict its observed properties (e.g., Kuznetsov et al 2012;Yu et al 2012).…”

Section: Auroral Radio Emissionmentioning

confidence: 99%

Radio Emission from Ultracool Dwarfs

Williams¹

2018

Handbook of Exoplanets

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This is an expanded version of a chapter submitted to the Handbook of Exoplanets, eds. Hans J. Deeg and Juan Antonio Belmonte, to be published by Springer Verlag.The 2001 discovery of radio emission from ultra-cool dwarfs (UCDs), the very lowmass stars and brown dwarfs with spectral types of ∼M7 and later, revealed that these objects can generate and dissipate powerful magnetic fields. Radio observations provide unparalleled insight into UCD magnetism: detections extend to brown dwarfs with temperatures 1000 K, where no other observational probes are effective. The data reveal that UCDs can generate strong (kG) fields, sometimes with a stable dipolar structure; that they can produce and retain nonthermal plasmas with electron acceleration extending to MeV energies; and that they can drive auroral current systems resulting in significant atmospheric energy deposition and powerful, coherent radio bursts. Still to be understood are the underlying dynamo processes, the precise means by which particles are accelerated around these objects, the observed diversity of magnetic phenomenologies, and how all of these factors change as the mass of the central object approaches that of Jupiter. The answers to these questions are doubly important because UCDs are both potential exoplanet hosts, as in the TRAPPIST-1 system, and analogues of extrasolar giant planets themselves.

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Electron-Beam-Induced Radio Emission From Ultracool Dwarfs

Cited by 14 publications

References 57 publications

Volume-limited radio survey of ultracool dwarfs

Volume-limited radio survey of ultracool dwarfs

Modelling the environment around five ultracool dwarfs via the radio domain

Radio Emission from Ultracool Dwarfs

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