Radio Emission from Ultracool Dwarfs

Williams, Peter K. G.

doi:10.1007/978-3-319-30648-3_171-1

Cited by 5 publications

(5 citation statements)

References 114 publications

(157 reference statements)

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“…Intensive observations of exoplanetary systems have, in turn, been carried out in the past decades and currently form a major objective of large ground-based radiotelescopes [31]. While still waiting for a confirmed detection, a few tens of stellar objects have already been detected at radio wavelengths, with bright, highly circularly polarized, bursts assigned to CMI [32]. The coolest of these (so-called ultracool dwarves, with spectral type later than M7) display bursty and quiescent emissions.…”

Section: Auroral Radio Emissionsmentioning

confidence: 99%

Auroral emissions from Uranus and Neptune

Lamy

2020

Phil. Trans. R. Soc. A.

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Uranus and Neptune possess highly tilted/offset magnetic fields whose interaction with the solar wind shapes unique twin asymmetric, highly dynamical, magnetospheres. These radiate complex auroral emissions, both reminiscent of those observed at the other planets and unique to the ice giants, which have been detected at radio and ultraviolet (UV) wavelengths to date. Our current knowledge of these radiations, which probe fundamental planetary properties (magnetic field, rotation period, magnetospheric processes, etc.), still mostly relies on Voyager 2 radio, UV and in situ measurements, when the spacecraft flew by each planet in the 1980s. These pioneering observations were, however, limited in time and sampled specific solar wind/magnetosphere configurations, which significantly vary at various timescales down to a fraction of a planetary rotation. Since then, despite repeated Earth-based observations at similar and other wavelengths, only the Uranian UV aurorae have been re-observed at scarce occasions by the Hubble Space Telescope. These observations revealed auroral features radically different from those seen by Voyager 2, diagnosing yet another solar wind/magnetosphere configuration. Perspectives for the in-depth study of the Uranian and Neptunian auroral processes, with implications for exoplanets, include follow-up remote Earth-based observations and future orbital exploration of one or both ice giant planetary systems. This article is part of a discussion meeting issue ‘Future exploration of ice giant systems’.

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Section: Auroral Radio Emissionsmentioning

confidence: 99%

Auroral emissions from Uranus and Neptune

Lamy

2020

Phil. Trans. R. Soc. A.

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“…A compilation of the L dwarfs with radio emission can be found in Williams (2018). The number of L dwarfs with known radio emission is currently nine, among which four are confirmed to have radio emission that varies with periods of 1 h time-scales.…”

Section: Previous Studies: X-ray and Radio Emissionmentioning

confidence: 99%

K2 Ultracool Dwarfs Survey – VI. White light superflares observed on an L5 dwarf and flare rates of L dwarfs

Paudel

Gizis

Mullan

et al. 2020

Monthly Notices of the Royal Astronomical Society

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$Kepler\, K2$ long cadence data are used to study white light flares in a sample of 45 L dwarfs. We identified 11 flares on 9 L dwarfs with equivalent durations of (1.3–198) h and total (UV/optical/IR) energies of ≥0.9 × 1032 erg. Two superflares with energies of >1033 erg were detected on an L5 dwarf (VVV BD001): this is the coolest object so far on which flares have been identified. The larger superflare on this L5 dwarf has an energy of 4.6 × 1034 erg and an amplitude of >300 times the photospheric level: so far, this is the largest amplitude flare detected by the Kepler/K2 mission. The next coolest star on which we identified a flare was an L2 dwarf: 2MASS J08585891+1804463. Combining the energies of all the flares which we have identified on 9 L dwarfs with the total observation time which was dedicated by Kepler to all 45 L dwarfs, we construct a composite flare frequency distribution (FFD). The FFD slope is quite shallow (−0.51 ± 0.17), consistent with earlier results reported by Paudel et al. for one particular L0 dwarf, for which the FFD slope was found to be −0.34. Using the composite FFD, we predict that, in early- and mid-L dwarfs, a superflare of energy 1033 erg occurs every 2.4 yr and a superflare of energy 1034 erg occurs every 7.9 yr. Analysis of our L dwarf flares suggests that magnetic fields of ≥0.13–1.3 kG are present on the stellar surface: such fields could suppress Type II radio bursts.

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“…Additionally, though the detection from exoplanets has yet to be confirmed, we have found such emissions from larger objects such as ultracool dwarfs, providing measurements of their magnetic field and insight into the presence of electrons into the MeV range [6] . The search for exo-magnetospheres at radio wavelengths with ground-based telescopes has become a hot topic.…”

Section: Auroral Processes and Current Systemsmentioning

confidence: 77%

The case for studying other planetary magnetospheres and atmospheres in Heliophysics

Cohen,

Arridge,

Azari

et al. 2023

Vol. 55, Issue 3 (Heliophysics 2024 Decadal Whitepapers)

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Heliophysics is the field that "studies the nature of the Sun, and how it influences the very nature of space -and, in turn, the atmospheres of planetary bodies and the technology that exists there." [1] However, NASA's Heliophysics Division tends to limit study of planetary magnetospheres and atmospheres to only those of Earth. This leaves exploration and understanding of space plasma physics at other worlds to the purview of the Planetary Science and Astrophysics Divisions. This is detrimental to the study of space plasma physics in general since, although some cross-divisional funding opportunities do exist, vital elements of space plasma physics can be best addressed by extending the expertise of Heliophysics scientists to other stellar and planetary magnetospheres. However, the diverse worlds within the solar system provide crucial environmental conditions that are not replicated at Earth but can provide deep insight into fundamental space plasma physics processes. Studying planetary systems with Heliophysics objectives, comprehensive instrumentation, and new grant opportunities for analysis and modeling would enable a novel understanding of fundamental and universal processes of space plasma physics. As such, the Heliophysics community should be prepared to consider, prioritize, and fund dedicated Heliophysics efforts to planetary targets to specifically study space physics and aeronomy objectives.

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Radio Emission from Ultracool Dwarfs

Cited by 5 publications

References 114 publications

Auroral emissions from Uranus and Neptune

Auroral emissions from Uranus and Neptune

K2 Ultracool Dwarfs Survey – VI. White light superflares observed on an L5 dwarf and flare rates of L dwarfs

The case for studying other planetary magnetospheres and atmospheres in Heliophysics

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