On the Star-Magnetosphere Interaction of Close-in Exoplanets

Ip, W.-H.; Kopp, A.; Hu, Jiumei

doi:10.1086/382274

Cited by 193 publications

(141 citation statements)

References 26 publications

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“…We therefore stress that r M here refers to a characteristic distance to the point where magnetic pressure equilibrium exists, which places an upper limit on the magnetospheric size, with the size at the nose being smaller if the stellar wind ram pressure is also taken into account. We note that the relative orientation of the stellar magnetic field with respect to the orientation of the planetary magnetic moment plays an important role in shaping the open-field-line region on the planet (e.g., Ip et al 2004;Zieger et al 2006;Kopp et al 2011;Sterenborg et al 2011;Saur et al 2013). Our purely magnetic pressure balance (Eq.…”

Section: Interaction Between the Planet And The Corona Of Its Host Starmentioning

confidence: 99%

“…On the stellar side, factors such as the thermal pressure, magnetic pressure (P B, ) and the ram pressure resulting from the relative motion between the planet and the coronal material can all contribute to setting the pressure equilibrium. The stellar-wind properties determine, for example, whether Earth-type magnetospheres surrounded by bow shocks or Ganymede-type magnetospheres with Alfvén wings are formed (Ip et al 2004;Zarka 2007;Kopp et al 2011;Sterenborg et al 2011;Saur et al 2013). To quantitatively evaluate this, the stellar wind density, temperature, magnetic field, and the relative velocity of the planet are required together with planetary magnetic characteristics.…”

Section: Interaction Between the Planet And The Corona Of Its Host Starmentioning

confidence: 99%

“…Kivelson & Russell 1995). However, for planets orbiting stars that are significantly more magnetised than the Sun or/and are located at close distances, the stellar magnetic pressure may play an important role in setting the magnetospheric limits (Ip et al 2004;Zieger et al 2006;Lovelace et al 2008;Lanza 2009;Vidotto et al 2009Vidotto et al , 2010bVidotto et al , 2012Vidotto et al , 2011bSterenborg et al 2011;Khodachenko et al 2012;Buzasi 2013). The extent of the magnetosphere of planets orbiting in the HZ of dM stars have been investigated by other authors (e.g.…”

Section: Introductionmentioning

confidence: 99%

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Effects of M dwarf magnetic fields on potentially habitable planets

Vidotto

Jardine

Morin

et al. 2013

A&A

147

161

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We investigate the effect of the magnetic fields of M dwarf (dM) stars on potentially habitable Earth-like planets. These fields can reduce the size of planetary magnetospheres to such an extent that a significant fraction of the planet's atmosphere may be exposed to erosion by the stellar wind. We used a sample of 15 active dM stars, for which surface magnetic-field maps were reconstructed, to determine the magnetic pressure at the planet orbit and hence the largest size of its magnetosphere, which would only be decreased by considering the stellar wind. Our method provides a fast means to assess which planets are most affected by the stellar magnetic field, which can be used as a first study to be followed by more sophisticated models. We show that hypothetical Earth-like planets with similar terrestrial magnetisation (∼1 G) orbiting at the inner (outer) edge of the habitable zone of these stars would present magnetospheres that extend at most up to 6 (11.7) planetary radii. To be able to sustain an Earth-sized magnetosphere, with the exception of only a few cases, the terrestrial planet would either (1) need to orbit significantly farther out than the traditional limits of the habitable zone; or else, (2) if it were orbiting within the habitable zone, it would require at least a magnetic field ranging from a few G to up to a few thousand G. By assuming a magnetospheric size that is more appropriate for the young-Earth (3.4 Gyr ago), the required planetary magnetic fields are one order of magnitude weaker. However, in this case, the polar-cap area of the planet, which is unprotected from transport of particles to/from interplanetary space, is twice as large. At present, we do not know how small the smallest area of the planetary surface is that could be exposed and would still not affect the potential for formation and development of life in a planet. As the star becomes older and, therefore, its rotation rate and magnetic field reduce, the interplanetary magnetic pressure decreases and the magnetosphere of planets probably expands. Using an empirically derived rotation-activity/magnetism relation, we provide an analytical expression for estimating the shortest stellar rotation period for which an Earth-analogue in the habitable zone could sustain an Earth-sized magnetosphere. We find that the required rotation rate of the early-and mid-dM stars (with periods 37-202 days) is slower than the solar one, and even slower for the late-dM stars ( 63-263 days). Planets orbiting in the habitable zone of dM stars that rotate faster than this have smaller magnetospheric sizes than that of the Earth magnetosphere. Because many late-dM stars are fast rotators, conditions for terrestrial planets to harbour Earth-sized magnetospheres are more easily achieved for planets orbiting slowly rotating early-and mid-dM stars.

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Section: Interaction Between the Planet And The Corona Of Its Host Starmentioning

confidence: 99%

Section: Interaction Between the Planet And The Corona Of Its Host Starmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Effects of M dwarf magnetic fields on potentially habitable planets

Vidotto

Jardine

Morin

et al. 2013

A&A

147

161

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“…6.5); in particular, its yet unmodeled interaction with HD 189733 (see e.g., Lecavelier des Etangs et al 2012) that could induce unexpected thermal patterns, e.g., asymmetric patterns in its BD. For example, magnetic star-planet interactions may lead to energy dissipation due to the stellar field penetration into the exoplanet envelope (e.g., Laine et al 2008) and to extensive energy injections into the auroral zones of the exoplanet from magnetic reconnections (e.g., Ip et al 2004) -similarly to the Jupiter-Io flux tube (e.g., Bigg 1964). However, such magnetic reconnections have so far been only observed at the stellar surface, in the form of chromospheric hot spots rotating synchronously with the companions (e.g., Shkolnik et al 2005;Lanza 2009).…”

Section: The Most Adequate Modelmentioning

confidence: 99%

Towards consistent mapping of distant worlds: secondary-eclipse scanning of the exoplanet HD 189733b

Wit

Gillon

Demory

et al. 2012

A&A

141

163

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Context. Mapping distant worlds is the next frontier for exoplanet infrared (IR) photometry studies. Ultimately, constraining spatial and temporal properties of an exoplanet atmosphere (e.g., its temperature) will provide further insight into its physics. For tidallylocked hot Jupiters that transit and are eclipsed by their host star, the first steps are now possible. Aims. Our aim is to constrain an exoplanet's (1) shape, (2) brightness distribution (BD) and (3) system parameters from its phase curve and eclipse measurements. In particular, we rely on the secondary-eclipse scanning which is obtained while an exoplanet is gradually masked by its host star. Methods. We use archived Spitzer/IRAC 8-µm data of HD 189733 (six transits, eight secondary eclipses, and a phase curve) in a global Markov chain Monte Carlo (MCMC) procedure for mitigating systematics. We also include HD 189733's out-of-transit radial velocity (RV) measurements to assess their incidence on the inferences obtained solely from the photometry. Results. We find a 6σ deviation from the expected occultation of a uniformly-bright disk. This deviation emerges mainly from a large-scale hot spot in HD 189733b's atmosphere, not from HD 189733b's shape. We indicate that the correlation of the exoplanet orbital eccentricity, e, and BD ("uniform time offset") does also depend on the stellar density, ρ , and the exoplanet impact parameter, b ("e-b-ρ -BD correlation"). For HD 189733b, we find that relaxing the eccentricity constraint and using more complex BDs lead to lower stellar/planetary densities and a more localized and latitudinally-shifted hot spot. We, therefore, show that the light curve of an exoplanet does not constrain uniquely its brightness peak localization. Finally, we obtain an improved constraint on the upper limit of HD 189733b's orbital eccentricity, e ≤ 0.011 (95% confidence), when including HD 189733's RV measurements. Conclusions. Reanalysis of archived HD 189733's data constrains HD 189733b's shape and BD at 8 µm. Our study provides new insights into the analysis of exoplanet light curves and a proper framework for future eclipse-scanning observations. In particular, observations of the same exoplanet at different wavelengths could improve the constraints on HD 189733's system parameters while ultimately yielding a large-scale time-dependent 3D map of HD 189733b's atmosphere. Finally, we discuss the perspective of extending our method to observations in the visible (e.g., Kepler data), in particular to better understand exoplanet albedos.

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“…Models predict that hot Jupiters could affect the activity of their host stars through either tidal or magneto-hydrodynamical interaction (e.g. Cuntz et al 2000 andIp et al 2004). Both effects strongly scale with the separation d between the two bodies (Saar et al 2004).…”

Section: Introductionmentioning

confidence: 99%

No X-rays from WASP-18

Pillitteri

Wolk

Sciortino

et al. 2014

A&A

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About 20% of the >1000 known exoplanets are Jupiter analogs orbiting very close to their parent stars. It is still under debate to what detectable level such hot Jupiters possibly affect the activity of the host stars through tidal or magnetic star-planet interaction. In this paper we report on an 87 ks Chandra observation of the hot Jupiter hosting star WASP-18. This system is composed of an F6 type star and a hot Jupiter of mass 10.4 M Jup orbiting in less than 20 hr around the parent star. On the basis of an isochrone fitting, WASP-18 is thought to be 600 Myr old and within the range of uncertainty of 0.5-2 Gyr. The star is not detected in X-rays down to a luminosity limit of 4 × 10 26 erg/s, which is more than two orders of magnitude lower than expected for a star of this age and mass. This value proves an unusual lack of activity for a star with an estimated age around 600 Myr. We argue that the massive planet can play a crucial role in disrupting the stellar magnetic dynamo created within its thin convective layers. Other additional 212 X-ray sources are detected in the Chandra image. We list them and briefly discuss their nature.

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On the Star-Magnetosphere Interaction of Close-in Exoplanets

Cited by 193 publications

References 26 publications

Effects of M dwarf magnetic fields on potentially habitable planets

Effects of M dwarf magnetic fields on potentially habitable planets

Towards consistent mapping of distant worlds: secondary-eclipse scanning of the exoplanet HD 189733b

No X-rays from WASP-18

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