Close-by planets and flares in their host stars

Abstract

The interaction between the magnetic fields of late-type stars and their close-by planets may produce stellar flares as observed in active binary systems. However, in spite of several claims, conclusive evidence is still lacking. We estimate the magnetic energy available in the interaction using analytical models to provide an upper bound to the expected flare energy. We investigate three different mechanisms leading to magnetic energy release. The first two can release an energy up to $(0.2-1.2)B_0^2{R}^3/\mu$, where $B_0$ is the surface field of the star, $R$ its radius, and $\mu$ the magnetic permeability of the plasma. They operate in young active stars whose coronae have closed magnetic field lines up to the distance of their close-by planets that can trigger the energy release. The third mechanism operates in weakly or moderately active stars having a coronal field with predominantly open field lines at the distance of their planets. The released energy is of the order of $(0.002-0.1)B_0^2{R}^3/\mu$ and depends on the ratio of the planetary to the stellar fields, thus allowing an indirect measurement of the former when the latter is known. We compute the released energy for different separations of the planet and different stellar parameters finding the conditions for the operation of the proposed mechanisms. An application to eight selected systems is presented. The computed energies and dissipation timescales are in agreement with flare observations in the eccentric system HD 17156 and in the circular systems HD 189733 and HD 179949. This kind of star-planet interaction can be unambiguously identified by the higher flaring frequency expected close to periastron in eccentric systems.

17 pages, 9 figures, 5 tables; accepted to Astronomy and Astrophysics

References in corpus (30)

• The On/Off Nature of Star-Planet Interactions
• Toroidal versus poloidal magnetic fields in Sun-like stars: a rotation threshold
• The Exoplanet Orbit Database II: Updates to exoplanets.org
• Early UV Ingress in WASP-12b: Measuring Planetary Magnetic Fields
• Magnetic Field Confinement in the Corona: The Role of Magnetic Helicity Accumulation
• Magnetospheric Structure and Atmospheric Joule Heating of Habitable Planets Orbiting M-dwarf Stars
• Magnetic games between a planet and its host star: the key role of topology
• MOST detects variability on tau Bootis possibly induced by its planetary companion
• The connection between stellar activity cycles and magnetic field topology
• The corona of HD 189733 and its X-ray activity
• A comparison of gyrochronological and isochronal age estimates for transiting exoplanet host stars
• A comprehensive statistical assessment of star-planet interaction
• The Evolving Magnetic Topology of $\tau$ Boötis
• Free Magnetic Energy in Solar Active Regions above the Minimum-Energy Relaxed State
• Studying stellar spin-down with Zeeman-Doppler magnetograms
• A decade of H$\alpha$ transits for HD 189733 b: stellar activity versus absorption in the extended atmosphere
• The hot Jupiter of the magnetically-active weak-line T Tauri star V830 Tau
• Interacting coronae of two T Tauri stars: first observational evidence for solar-like helmet streamers
• FUV variability of HD 189733. Is the star accreting material from its hot Jupiter?
• Assessing magnetic torques and energy fluxes in close-in star-planet systems
• No X-rays from WASP-18. Implications for its age, activity, and the influence of its massive hot Jupiter
• Revisiting the correlation between stellar activity and planetary surface gravity
• The dependence of the helicity bound of force-free magnetic fields on boundary conditions
• Temporal variability of the wind from the star τ Boötis
• On the correlation between stellar chromospheric flux and the surface gravity of close-in planets
• The effect of ISM absorption on stellar activity measurements and its relevance for exoplanet studies
• Time-resolved UVES observations of a stellar flare on the planet host HD 189733 during primary transit
• Is the activity level of HD 80606 influenced by its eccentric planet?
• The magnetic properties of the planet host star Kepler-78
• Separable solutions of force-free spheres and applications to solar active regions

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• One year of AU Mic with HARPS: II -- stellar activity and star-planet interaction
• Time-variable electromagnetic star-planet interaction: The TRAPPIST-1 system as an exemplary case
• Chasing star-planet magnetic interactions: the case of Kepler-78
• Searching for flaring star-planet interactions in AU Mic TESS observations
• Short term variability of DS Tuc A observed with TESS
• A statistical search for Star-Planet Interaction in the UltraViolet using GALEX
• Superflares on Giant Stars
• The corona of GJ 1151 in the context of star-planet interaction
• Star-Planet Interaction: Wave Structures and Wing-Wing Interaction
• The milliarcsecond-scale radio structure of AB Dor A
• Observational features of exoplanetary synchrotron radio bursts
• EvryFlare IV: Detection of periodicity in flare occurrence from cool stars with TESS
• Constraining an exoplanets magnetic field using star-planet interactions
• Spectroscopic Characterization of LOFAR Radio-emitting M dwarfs
• Star-planet magnetic interactions in photoevaporating exoplanets: enhanced power due to atmospheric escape