The Magnetosphere of the Ultracool Dwarf Denis 1048–3956

Ravi, Vikram; Hallinan, Gregg; Hobbs, G.; Champion, D. J.

doi:10.1088/2041-8205/735/1/l2

Cited by 30 publications

(36 citation statements)

References 32 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The smaller frequency coverage of our observations could be the cause of this difference. However, similar to 2MASS J0339-3525, the 4-9 GHz emission of 2MASS J1048-3956 is variable on longtime scales where the radio emission previously observed by Ravi et al (2011) has a slightly higher flux density and is circularly polarised with a polarisation fraction of 0.25-0.4. Long-term variability in the measured flux densities and polarisation of UCDs has been observed in several other cases (McLean et al 2012) and may indicate a significant change in the physical characteristics of the emitting regions in these sources.…”

Section: Spectral Indicesmentioning

confidence: 55%

“…This selection of sources consists of 8 M dwarfs and 7 L dwarfs, with spectral types ranging from M7.0 to L8.0. Additionally, this selection of sources includes 3 known radio loud ultracool dwarfs: 2MASS J1456-2809 (Burgasser & Putman 2005;Osten & Wolk 2009), 2MASS J10481463-3956062 (Burgasser & Putman 2005;Ravi et al 2011), and 2MASSI J0339352-352544 (Berger et al 2001). Further details about the selected survey targets are given in Table 1.…”

Section: Observations and Data Reductionmentioning

confidence: 99%

“…This flux density variation could also be related to a variation in the spectral index. The quiescent radio emission from 2MASS J1048-3956 has been studied over a wide range of radio frequencies (∼4.0-20 GHz) by Ravi et al (2011) who fit a spectral index of α=1.71±0.09 to the observed radio emission. The smaller frequency coverage of our observations could be the cause of this difference.…”

Section: Spectral Indicesmentioning

confidence: 99%

See 2 more Smart Citations

Radio detections of southern ultracool dwarfs

Lynch

Murphy

Ravi

et al. 2016

Mon. Not. R. Astron. Soc.

Self Cite

View full text Add to dashboard Cite

We report the results of a volume-limited survey using the Australia Telescope Compact Array to search for transient and quiescent radio emission from 15 southern hemisphere ultracool dwarfs. We detect radio emission from 2MASSW J0004348-404405 increasing the number of radio loud ultracool dwarfs to 22. We also observe radio emission from 2MASS J10481463-3956062 and 2MASSI J0339352-352544, two sources with previous radio detections. The radio emission from the three detected sources shows no variability or flare emission. Modelling this quiescent emission we find that it is consistent with optically thin gyrosynchrotron emission from a magnetosphere with an emitting region radius of (1-2)R * , magnetic field inclination 20 • -80 • , field strength ∼10 -200 G, and power-law electron density ∼10 4 -10 8 cm −3 . Additionally, we place upper limits on four ultracool dwarfs with no previous radio observations. This increases the number of ultracool dwarfs studied at radio frequencies to 222. Analysing general trends of the radio emission for this sample of 15 sources, we find that the radio activity increases for later spectral types and more rapidly rotating objects. Furthermore, comparing the ratio of the radio to X-ray luminosities for these sources, we find 2MASS J10481463-3956062 and 2MASSI J0339352-352544 violate the Güdel-Benz relation by more than two orders of magnitude.

show abstract

Section: Spectral Indicesmentioning

confidence: 55%

Section: Observations and Data Reductionmentioning

confidence: 99%

Section: Spectral Indicesmentioning

confidence: 99%

See 1 more Smart Citation

Radio detections of southern ultracool dwarfs

Lynch

Murphy

Ravi

et al. 2016

Mon. Not. R. Astron. Soc.

Self Cite

View full text Add to dashboard Cite

show abstract

“…hot material of MK temperatures is present. Further complicating the picture, the X-ray emitting plasma of DENIS 1048-3956 may not be associated with the radio structures: Ravi et al (2011) ascribed the gyrosynchrotron radio component to emission from electrons streaming out in open field lines that cannot confine coronal plasma, while the pulsed radio component represents ECM emission (Burgasser & Putman 2005), i.e. it has a physically different origin from the X-ray photons.…”

Section: Discussionmentioning

confidence: 99%

“…Mass motions related to the flare were inferred from the detection of blueshifts in some emission lines, and interpreted as a rising gas cloud. Radio bursts were observed on DENIS 1048-3956 that are indicative of ECM emission (Burgasser & Putman 2005), but its radio spectrum shows a negative slope typical of gyrosynchrotron emission (Ravi et al 2011). No X-ray emission could be detected with ROSAT (Schmitt & Liefke 2004).…”

Section: Introductionmentioning

confidence: 99%

The ultracool dwarf DENIS-P J104814.7-395606

Stelzer

Alcalá

Biazzo

et al. 2012

A&A

View full text Add to dashboard Cite

Context. Several diagnostics ranging from the radio to the X-ray band are suitable for investigating the magnetic activity of late-type stars. Empirical connections between the emission at different wavelengths place constraints on the nature and efficiency of the emission mechanism and the physical conditions in different atmospheric layers. The activity of ultracool dwarfs, at the low-mass end of the main-sequence, is poorly understood. Aims. We perform a multi-wavelength study of one of the nearest M9 dwarfs, DENIS-P J104814.7-395606 (4 pc), to examine its position within the group of magnetically active ultracool dwarfs, and, in general, advance our understanding of these objects by comparing them to early-M type dwarf stars and the Sun. Methods. We obtained an XMM-Newton observation of DENIS-P J104814.7-395606 and a broad-band spectrum from the ultraviolet to the near-infrared with X-Shooter. From this dataset, we derive the X-ray properties, stellar parameters, kinematics, and the emission-line spectrum tracing chromospheric activity. We integrate these data by compiling the activity parameters of ultracool dwarfs from the literature. Results. Our deep XMM-Newton observation provides the first X-ray detection of DENIS-P J104814.7-395606 (log L x = 25.1), as well as the first measurement of its V band brightness (V = 17.35 mag). The flux-flux relations between X-ray and chromospheric activity indicators are here for the first time extended into the regime of the ultracool dwarfs. The approximate agreement of DENIS-P J104814.7-395606 and other ultracool dwarfs with flux-flux relations for early-M dwarfs suggests that the same heating mechanisms work in the atmospheres of ultracool dwarfs, albeit weaker as judged from their lower fluxes. The observed Balmer decrements of DENIS 1048-3956 are compatible with optically thick plasma in local thermal equilibrium (LTE) at low, nearly photospheric temperature or optically thin LTE plasma at 20 000 K. Describing the decrements with case B recombination requires different emitting regions for Hα and the higher Balmer lines. The high observed Hα/Hβ flux ratio is also poorly fitted by the optically thin models. We derive a similarly high value for the Hα/Hβ ratio of vB 10 and LHS 2065 and conclude that this may be a characteristic of ultracool dwarfs. We add DENIS-P J104814.7-395606 to the list of ultracool dwarfs detected in both the radio and the X-ray band. The Benz-Güdel relation between radio and X-ray luminosity of late-type stars is well-known to be violated by ultracool dwarfs. We speculate on the presence of two types of ultracool dwarfs with distinct radio and X-ray behaviors.

show abstract

Radio Emission from Ultracool Dwarfs

Williams¹

2018

Handbook of Exoplanets

View full text Add to dashboard Cite

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.

show abstract

The Magnetosphere of the Ultracool Dwarf Denis 1048–3956

Cited by 30 publications

References 32 publications

Radio detections of southern ultracool dwarfs

Radio detections of southern ultracool dwarfs

The ultracool dwarf DENIS-P J104814.7-395606

Radio Emission from Ultracool Dwarfs

Contact Info

Product

Resources

About