Time-scales of close-in exoplanet radio emission variability

See, Victor; Jardine, M.; Farès, R.; Donati, J.‐F.; Moutou, C.

doi:10.1093/mnras/stv896

Cited by 55 publications

(33 citation statements)

References 57 publications

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“…In this work we will use a similar wind model to that of See et al (2015a). For the Sun, the wind speed is known to be correlated with the amount of field line divergence of the magnetic field lines (Levine et al 1977;Wang & Sheeley 1990, 1991.…”

Section: Wind Speed Density and Mass-loss Ratementioning

confidence: 99%

Studying stellar spin-down with Zeeman–Doppler magnetograms

See

Jardine

Vidotto

et al. 2016

Mon. Not. R. Astron. Soc.

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Magnetic activity and rotation are known to be intimately linked for low-mass stars. Understanding rotation evolution over the stellar lifetime is therefore an important goal within stellar astrophysics. In recent years, there has been increased focus on how the complexity of the stellar magnetic field affects the rate of angular momentum-loss from a star. This is a topic that Zeeman-Doppler imaging (ZDI), a technique that is capable of reconstructing the large-scale magnetic field topology of a star, can uniquely address.Using a potential field source surface model, we estimate the open flux, mass loss-rate and angular momentum-loss rates for a sample of 66 stars that have been mapped with ZDI. We show that the open flux of a star is predominantly determined by the dipolar component of its magnetic field for our choice of source surface radius. We also show that, on the main sequence, the open flux, mass-and angular momentum-loss rates increase with decreasing Rossby number. The exception to this rule is stars less massive than 0.3 M . Previous work suggests that low mass M dwarfs may possess either strong, ordered and dipolar fields or weak and complex fields. This range of field strengths results in a large spread of angular momentum-loss rates for these stars and has important consequences for their spin down behaviour. Additionally, our models do not predict a transition in the mass-loss rates at the so called wind dividing line noted from Lyα studies.

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Section: Wind Speed Density and Mass-loss Ratementioning

confidence: 99%

Studying stellar spin-down with Zeeman–Doppler magnetograms

See

Jardine

Vidotto

et al. 2016

Mon. Not. R. Astron. Soc.

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“…These are calculated using the PFFS method of Altschuler & Newkirk (1969) to determine the 3D coronal magnetic field geometry and the relation of Arge & Pizzo (2000) to determine the stellar wind velocity from the expansion of the magnetic field lines. The stellar wind density is obtained by scaling the solar wind density at 1 AU in same manner as Jardine & Collier Cameron (2008) and See et al (2015a). The mass loss rate then follows by integrating over a spherical surface.…”

Section: Input Parametersmentioning

confidence: 99%

Prominence formation and ejection in cool stars

D’Angelo

Jardine

See

2017

Monthly Notices of the Royal Astronomical Society: Letters

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The observational signatures of prominences have been detected in single and binary G and K type stars for many years now, but recently this has been extended to the M dwarf regime. Prominences carry away both mass and angular momentum when they are ejected and the impact of this mass on any orbiting planets may be important for the evolution of exoplanetary atmospheres. By means of the classification used in the massive star community, that involves knowledge of two parameters (the corotation and Alfvén radii, r K and r A ), we have determined which cool stars could support prominences. From a model of mechanical support, we have determined that the prominence mass m p /M = (E M /E G )(r /r K ) 2 F where E M B 2 r 3 and E G = GM 2 /r are magnetic and gravitational energies and F is a geometric factor. Our calculated masses and ejection frequencies (typically 10 16 − 10 17 g and 0.4 d, respectively) are consistent with observations and are sufficient to ensure that an exoplanet orbiting in the habitable zone of an M dwarf could suffer frequent impacts.

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“…The interaction leads to particle acceleration that is manifested in auroral emissions and magnetosphere-ionosphere field aligned currents, both associated with known mechanisms to generate radio waves (e.g., Zarka 2007;Lazio & Farrell 2007;Grießmeier et al 2007;Vidotto et al 2015;See et al 2015;Nichols & Milan 2016;Alvarado-Gómez et al 2016a;Burkhart & Loeb 2017;Turnpenney et al 2018;Lynch et al 2018). See et al (2015) have used Zeeman-Doppler imaging (ZDI) maps to estimate the temporal variations of radio emissions from exoplanets directly from the magnetic maps, and using some empirical estimation for the radio power (assuming planetary auroral emissions). Llama et al (2018) presented a more detailed calculation of the coronal radio emissions from V374 Peg using potential field approximation, and hydrostatic coronal density (non-MHD solution).…”

Section: Introductionmentioning

confidence: 99%

Exoplanet Modulation of Stellar Coronal Radio Emission

Cohen

Moschou

Glocer

et al. 2018

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The search for exoplanets in the radio bands has been focused on detecting radio emissions produced by the interaction between magnetized planets and the stellar wind (auroral emission). Here we introduce a new tool, which is part of our MHD stellar corona model, to predict the ambient coronal radio emission and its modulations induced by a close planet. For simplicity, the present work assumes that the exoplanet is stationary in the frame rotating with the stellar rotation. We explore the radio flux modulations using a limited parameter space of idealized cases by changing the magnitude of the planetary field, its polarity, the planetary orbital separation, and the strength of the stellar field. We find that the modulations induced by the planet could be significant and observable in the case of hot Jupiter planets -above 100% modulation with respect to the ambient flux in the 10 − 100 M Hz range in some cases, and 2-10% in the frequency bands above 250 M Hz for some cases. Thus, our work indicates that radio signature of exoplanets might not be limited to low-frequency radio range. We find that the intensity modulations are sensitive to the planetary magnetic field polarity for shortorbit planets, and to the stellar magnetic field strength for all cases. The new radio tool, when applied to real systems, could provide predictions for the frequency range at which the modulations can be observed by current facilities.

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Time-scales of close-in exoplanet radio emission variability

Cited by 55 publications

References 57 publications

Studying stellar spin-down with Zeeman–Doppler magnetograms

Studying stellar spin-down with Zeeman–Doppler magnetograms

Prominence formation and ejection in cool stars

Exoplanet Modulation of Stellar Coronal Radio Emission

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