The stable magnetic field of the fully convective star V374 Peg

Morin, J.; Donati, J.‐F.; Forveille, T.; Delfosse, X.; Dobler, Wolfgang; Petit, P.; Jardine, M.; Cameron, A. Collier; Li, Albert; Manset, N.; Dintrans, B.; Chabrier, G.; Valenti, Jeff A.

doi:10.1111/j.1365-2966.2007.12709.x

Cited by 157 publications

(144 citation statements)

References 30 publications

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“…In fact, Zeeman Doppler Imaging by Morin et al (2008) has shown that the magnetic topology for an M 4 dwarf is stable on a time-scale of 1 yr. Such information on the magnetic field is crucial to understanding the means by which persistent levels of ECM emission are sustained in the magnetospheres of UCDs.…”

Section: Resultsmentioning

confidence: 99%

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: 99%

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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“…The M4 dwarf V374 Peg was selected as the first target for this campaign as it has been confirmed to possess a large-scale magnetic field with a dominant dipolar component stable over timescales > 1 year [8,9]. Most importantly, the multi-epoch ZDI observations have allowed the period of rotation of the star to be determined with sufficient accuracy to allow direct correlation of any radio light curves to the putative orientation of the large-scale magnetic field at the time of the radio observations.…”

Section: Mapping the Radio Coronae Of Active M Dwarfsmentioning

confidence: 99%

Mapping the Radio Coronae of Cool Stars and Brown Dwarfs

Hallinan

Doyle

Antonova³

et al. 2009

AIP Conference Proceedings

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Abstract. The pulsing radio emission detected from ultracool dwarfs can be used as a powerful diagnostic of magnetic field strengths and topologies at and below the substellar boundary. Studies thus far have confirmed magnetic field strengths of 3 kG for two late M dwarfs and 1.7 kG for an L3.5 dwarf, the latter being the first confirmation of kG magnetic fields for an L dwarf. Ongoing long term monitoring of the radio pulses will also investigate the stability of the associated largescale magnetic fields over timescales > 1 year. We also present the preliminary results of a lengthy radio monitoring campaign of the rapidly rotating M4 star V374 Peg, with the resulting light curves phased with magnetic maps previously obtained through Zeeman Doppler Imaging. The radio emission from V374 Peg is strongly modulated by the large scale dipolar magnetic field, with two clear peaks in the radio light curve per period of rotation, occurring when the dipolar field lies in the plane of the sky. These results provide strong evidence that the electron cyclotron maser instability plays a pivotal role in the production of quiescent radio emission from V374 Peg, representing a significant departure from the accepted model of gyrosynchrotron emission as the dominant source of quiescent radio emission from active M dwarfs.

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“…Turbulent dynamos operating in other stars produce strong magnetic fields and are able to transform poloidal into toroidal fields, and vice versa. Morin et al (2008) showed that the M4 dwarf V374 Peg exhibits a strong magnetic field showing only weak signatures of DR. This effect becomes even more important when stars become fully convective (Morin et al 2010).…”

Section: Introductionmentioning

confidence: 99%

Rotation and differential rotation of activeKeplerstars

Reinhold

Reiners

Basri

2013

A&A

350

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Context. The Kepler space telescope monitors more than 160 000 stars with an unprecedented precision providing the opportunity to study the rotation of thousands of stars. Aims. We present rotation periods for thousands of active stars in the Kepler field derived from Q3 data. In most cases a second period close to the rotation period was detected that we interpreted as surface differential rotation (DR). We show how the absolute and relative shear (ΔΩ and α = ΔΩ/Ω, respectively) correlate with rotation period and effective temperature. Methods. Active stars were selected from the whole sample using the range of the variability amplitude. To detect different periods in the light curves we used the Lomb-Scargle periodogram in a pre-whitening approach to achieve parameters for a global sine fit. The most dominant periods from the fit were associated to different surface rotation periods. Our purely mathematical approach is capable of detecting different periods but cannot distinguish between the physical origins of periodicity. We ascribe the existence of different periods to DR, but spot evolution could also play a role. Because of the large number of stars the period errors are estimated statistically. We thus cannot exclude the existence of false positives among our periods.Results. In our sample of 40 661 active stars we found 24 124 rotation periods P 1 between 0.5 and 45 days, with a mean of P 1 = 16.3 days. The distribution of stars with 0.5 < B − V < 1.0 and ages derived from angular momentum evolution that are younger than 300 Myr is consistent with a constant star-formation rate; the detection among older stars is incomplete probably because of our active sample selection. A second period P 2 within ±30% of the rotation period P 1 was found in 18 616 stars (77.2%). Attributing these two periods to DR we found that for active stars other than the Sun the relative shear α increases with rotation period, and slightly decreases with effective temperature. The absolute shear ΔΩ slightly increases from ΔΩ = 0.079 rad d −1 at T eff = 3500 K to ΔΩ = 0.096 rad d −1 at T eff = 6000 K. Above 6000 K, ΔΩ shows much larger scatter. The dependence of ΔΩ on rotation period is weak over a large period range. Conclusions. Latitudinal differential rotation measured for the first time in more than 18 000 stars provides a comprehensive picture of stellar surface shear. This picture is consistent with major predictions from mean-field theory, and seems to support these models. To what extent our observations are prone to false positives and selection bias has not been fully explored, and needs to be addressed using other data, including the full Kepler time coverage.

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The stable magnetic field of the fully convective star V374 Peg

Cited by 157 publications

References 30 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

Mapping the Radio Coronae of Cool Stars and Brown Dwarfs

Rotation and differential rotation of activeKeplerstars

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