Rotational Modulation of M/L Dwarfs due to Magnetic Spots

Lane, Caoilfhionn; Hallinan, Gregg; Zavala, R. T.; Butler, R. P.; Boyle, R. P.; Bourke, S.; Antonova, A.; Doyle, J. G.; Vrba, F. J.; Golden, Aaron

doi:10.1086/523041

Cited by 40 publications

(87 citation statements)

References 17 publications

(14 reference statements)

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“…This is a second epoch observation of pulsed radio emission from TVLM 513, thus suggesting that the emission mechanism is stable on long times scales. From previous observations we know that the rotation period is ≈1.96 h (Hallinan et al 2006;Lane et al 2007). The main difference between the present data and the 2006 data reported by Hallinan et al (2007) is that the intervals of activity are longer, typically spread over 0.25 phase, comprising of several pulses.…”

Section: Resultsmentioning

confidence: 90%

“…The 8.4 GHz observation had an average flux of 228 μJy; however due to sequential sampling of three different frequencies, the time resolution was not sufficient to allow a variability study. In January 2005, Hallinan et al (2006) observed the same target simultaneously at 8.4 GHz and 4.9 GHz for a total of 5 h. These authors reported a periodicity at both frequencies of ≈2 h (later confirmed as the rotation period of the dwarf, Lane et al 2007), with a ≈400 μJy flux at 8.4 GHz. The first report of pulsed emission from TVLM 513 was by Hallinan et al (2007) (2008) report a nonperiodicity in the pulses/flaring activity (see later).…”

Section: Introductionmentioning

confidence: 89%

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Phase connecting multi-epoch radio data for the ultracool dwarf TVLM 513-46546

Doyle¹,

Antonova

Marsh

et al. 2010

A&A

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Context. Radio data obtained for the ultracool dwarf TVLM 513-46546 has indicated a rotation period of ≈1.96 h via regular radio pulses, but how stable is this period. This has major implications regarding the stability of the magnetic field structures responsible for the radio emission from the ultracool dwarf. Aims. The aim of the present work is to investigate the stability of this rotation period using two datasets taken ≈40 days apart, some 12 months after the first report of periodical pulses in the radio data. Methods. Here we use a Bayesian analysis method which is a statistical procedure that endeavours to estimate the parameters of an underlying model probability distribution based on the observed data. Results. Periodical pulses are detected in datasets taken in April and June 2007, with the pulses being confined to a narrow range in the rotation period. This is in contradiction to a previous report of only aperiodic activity in the April 2007 dataset, while in fact both datasets have a periodic signal with a false alarm probability 10 −12 . These two datasets are then used to derive a more accurate period (previously determined to be 1.96 h) of 1.96733 ± 0.00002 h. Conclusions. The similarly in the burst structure in datasets taken several weeks apart point towards the stability of an electric field structure which is somehow generated and sustained within the magnetosphere of the ultracool dwarf. The derived period of 1.96733 h is consistent with the period derived via radio and optical data taken some 12 months prior to the present observations and implies the near phase constancy of the pulsed emission. This suggest the presence of stable large-scale magnetic fields on timescales of more than 1 year. The characteristics of the pulses suggest that they are produced by the electron cyclotron maser (ECM) instability.

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Section: Resultsmentioning

confidence: 90%

Section: Introductionmentioning

confidence: 89%

Phase connecting multi-epoch radio data for the ultracool dwarf TVLM 513-46546

Doyle¹,

Antonova

Marsh

et al. 2010

A&A

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“…Perhaps the most plausible possibility is to obtain stellar inclinations from spectroscopic v sin i measurements. For this, the true rotational period of the star could be determined from photometric modulations caused by spots (Messina & Guinan 2003;Lane et al 2007) or a modulation of the Ca ii H and K emission fluxes (Noyes et al 1984), and the stellar radius could be obtained from stellar models. The major shortcoming of this method arises from the uncertainties in all the ingredients: v sin i, stellar rotational period and stellar radius.…”

Section: Introductionmentioning

confidence: 99%

Optimizing exoplanet transit searches around low-mass stars with inclination constraints

Herrero

Ribas

Jordi

et al. 2012

A&A

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Aims. We investigate a method to increase the efficiency of a targeted exoplanet search with the transit technique by preselecting a subset of candidates from large catalogs of stars. Assuming spin-orbit alignment, this can be achieved by considering stars that have a higher probability to be oriented nearly equator-on (inclination close to 90 • ). Methods. We used activity-rotation velocity relations for low-mass stars with a convective envelope to study the dependence of the position in the activity-v sin i diagram on the stellar axis inclination. We composed a catalog of G-, K-, M-type main-sequence simulated stars using isochrones, an isotropic inclination distribution and empirical relations to obtain their rotation periods and activity indexes. Then the activity-v sin i diagram was completed and statistics were applied to trace the areas containing the higher ratio of stars with inclinations above 80 • . A similar statistics was applied to stars from real catalogs with log(R HK ) and v sin i data to find their probability of being oriented equator-on. Results. We present our method to generate the simulated star catalog and the subsequent statistics to find the highly inclined stars from real catalogs using the activity-v sin i diagram. Several catalogs from the literature are analyzed and a subsample of stars with the highest probability of being equator-on is presented. Conclusions. Assuming spin-orbit alignment, the efficiency of an exoplanet transit search in the resulting subsample of probably highly inclined stars is estimated to be two to three times higher than with a general search without preselection.

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“…Variability has been reported in a number of L dwarfs (Clarke, Tinney, & Covey 2002;Koen 2006;Lane et al 2007;Heinze et al 2013). The amplitudes are typically ∼1% and the vari- Table 1.…”

Section: Variabilitymentioning

confidence: 99%

The Dawes Review 3: The Atmospheres of Extrasolar Planets and Brown Dwarfs

Bailey

2014

Publ. Astron. Soc. Aust.

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The last few years has seen a dramatic increase in the number of exoplanets known and in the range of methods for characterising their atmospheric properties. At the same time, new discoveries of increasingly cooler brown dwarfs have pushed down their temperature range which now extends down to Y-dwarfs of < 300 K. Modelling of these atmospheres has required the development of new techniques to deal with the molecular chemistry and clouds in these objects. The atmospheres of brown dwarfs are relatively well understood, but some problems remain, in particular the behavior of clouds at the L/T transition. Observational data for exoplanet atmosphere characterisation is largely limited to giant exoplanets that are hot because they are near to their star (hot Jupiters) or because they are young and still cooling. For these planets there is good evidence for the presence of CO and H2O absorptions in the IR. Sodium absorption is observed in a number of objects. Reflected light measurements show that some giant exoplanets are very dark, indicating a cloud free atmosphere. However, there is also good evidence for clouds and haze in some other planets. It is also well established that some highly irradiated planets have inflated radii, though the mechanism for this inflation is not yet clear. Some other issues in the composition and structure of giant exoplanet atmospheres such as the occurrence of inverted temperature structures, the presence or absence of CO2and CH4, and the occurrence of high C/O ratios are still the subject of investigation and debate.

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Rotational Modulation of M/L Dwarfs due to Magnetic Spots

Cited by 40 publications

References 17 publications

Phase connecting multi-epoch radio data for the ultracool dwarf TVLM 513-46546

Phase connecting multi-epoch radio data for the ultracool dwarf TVLM 513-46546

Optimizing exoplanet transit searches around low-mass stars with inclination constraints

The Dawes Review 3: The Atmospheres of Extrasolar Planets and Brown Dwarfs

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