Assessing Magnetic Torques and Energy Fluxes in Close-in Star–planet Systems

Strugarek, Antoine

doi:10.3847/1538-4357/833/2/140

Cited by 69 publications

(48 citation statements)

References 67 publications

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“…The next step will be to directly couple stellar evolution to orbital evolution code using the frequency-averaged tidal dissipation formalism to fully study the possible retro-action of tides and magnetic interactions on the internal structure and rotation of both stars and planets (for instance, using the prescriptions derived by Strugarek et al 2014, Strugarek 2016, Bolmont & Mathis 2016and Gallet et al 2017). In addition, we will take into account realistic density profiles in the convective envelope of low-mass stars (e.g.…”

Section: Resultsmentioning

confidence: 99%

Tidal dissipation in rotating low-mass stars and implications for the orbital evolution of close-in planets

Gallet

Bolmont

Mathis

et al. 2017

A&A

131

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Context. Star-planet interactions must be taken into account in stellar models to understand the dynamical evolution of close-in planets. The dependence of the tidal interactions on the structural and rotational evolution of the star is of peculiar importance and should be correctly treated. Aims. We quantify how tidal dissipation in the convective envelope of rotating low-mass stars evolves from the pre-main sequence up to the red-giant branch depending on the initial stellar mass. We investigate the consequences of this evolution on planetary orbital evolution. Methods. We couple the tidal dissipation formalism described in Mathis (2015) to the stellar evolution code STAREVOL and apply it to rotating stars with masses between 0.3 and 1.4 M ⊙ . As a first step, this formalism assumes a simplified bi-layer stellar structure with corresponding averaged densities for the radiative core and the convective envelope. We use a frequency-averaged treatment of the dissipation of tidal inertial waves in the convection zone (we neglect the dissipation of tidal gravity waves in the radiation zone). In addition, we generalize the work of Bolmont & Mathis (2016) by following the orbital evolution of close-in planets using the new tidal dissipation predictions for advanced phases of stellar evolution. Results. On the pre-main sequence the evolution of tidal dissipation is controlled by the evolution of the internal structure of the contracting star. On the main-sequence it is strongly driven by the variation of surface rotation that is impacted by magnetized stellar winds braking. The main effect of taking into account the rotational evolution of the stars is to lower the tidal dissipation strength by about four orders of magnitude on the main-sequence, compared to a normalized dissipation rate that only takes into account structural changes. Conclusions. The evolution of the dissipation strongly depends on the evolution of the internal structure and rotation of the star. From the pre-main sequence up to the tip of the red-giant branch, it varies by several orders of magnitude, with strong consequences for the orbital evolution of close-in massive planets. These effects are the strongest during the pre-main sequence, implying that the planets are mainly sensitive to the star's early history.

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Section: Resultsmentioning

confidence: 99%

Tidal dissipation in rotating low-mass stars and implications for the orbital evolution of close-in planets

Gallet

Bolmont

Mathis

et al. 2017

A&A

131

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“…The similarities of the absorption signatures in Visit B, D, and E at low velocities suggest that the dynamics of the neutral hydrogen layer close to the planet remains controlled by the same mechanism. The larger velocities of the red wing signature in Visit E suggest that we probe neutral hydrogen gas moving farther from the planet, possibly a stream accreting toward the star revealed by the enhancement in neutral hydrogen abundance (Lai et al 2010;Lanza 2014, Matsakos et al 2015Strugarek 2016). Such a stream could yield transit signatures in the Balmer lines at even larger distance from the planet, as suggested by the detection of pre-and post-transit absorption in ground-based optical observations (see Cauley et al 2017 and references within).…”

Section: Visit Ementioning

confidence: 99%

MOVES III. Simultaneous X-ray and ultraviolet observations unveiling the variable environment of the hot Jupiter HD 189733b

Bourrier

Wheatley

Étangs

et al. 2020

Monthly Notices of the Royal Astronomical Society

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In this third paper of the MOVES (Multiwavelength Observations of an eVaporating Exoplanet and its Star) programme, we combine Hubble Space Telescope far-ultraviolet observations with XMM-Newton/Swift X-ray observations to measure the emission of HD 189733 in various FUV lines, and its soft X-ray spectrum. Based on these measurements we characterise the interstellar medium toward HD 189733 and derive semi-synthetic XUV spectra of the star, which are used to study the evolution of its high-energy emission at five different epochs. Two flares from HD 189733 are observed, but we propose that the long-term variations in its spectral energy distribution have the most important consequences for the environment of HD 189733b. Reduced coronal and wind activity could favour the formation of a dense population of Si 2+ atoms in a bow-shock ahead of the planet, responsible for pre-and in-transit absorption measured in the first two epochs. In-transit absorption signatures are detected in the Lyman-α line in the second, third and fifth epochs, which could arise from the extended planetary thermosphere and a tail of stellar wind protons neutralised via charge-exchange with the planetary exosphere. We propose that increases in the X-ray irradiation of the planet, and decreases in its EUV irradiation causing lower photoionisation rates of neutral hydrogen, favour the detection of these signatures by sustaining larger densities of H 0 atoms in the upper atmosphere and boosting charge-exchanges with the stellar wind. Deeper and broader absorption signatures in the last epoch suggest that the planet entered a different evaporation regime, providing clues as to the link between stellar activity and the structure of the planetary environment.

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“…where P t is the stellar wind total pressure at the planetary orbit, M a the alfvénic Mach number, and Λ p the pressure ratio between the magnetic pressure in the magnetosphere of the planet and the wind pressure P t . The coefficients A 0 , χ and ξ have been calibrated from a set of 3D numerical simulations in Strugarek (2016), and depend on the magnetic topology of the interaction. We will consider in this letter only the aligned configuration, which maximizes the magnetic torque.…”

Section: Dipolar Interactionmentioning

confidence: 99%

The Fate of Close-in Planets: Tidal or Magnetic Migration?

Strugarek

Bolmont

Mathis

et al. 2017

ApJL

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Planets in close-in orbits interact magnetically and tidally with their host stars. These interactions lead to a net torque that makes close-in planets migrate inward or outward depending on their orbital distance. We compare systematically the strength of magnetic and tidal torques for typical observed star-planet systems (T-Tauri & hot Jupiter, M dwarf & Earth-like planet, K star & hot Jupiter) based on state-of-the-art scaling-laws. We find that depending on the characteristics of the system, tidal or magnetic effects can dominate. For very close-in planets, we find that both torques can make a planet migrate on a timescale as small as 10 to 100 thousands of years. Both effects thus have to be taken into account when predicting the evolution of compact systems.

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Assessing Magnetic Torques and Energy Fluxes in Close-in Star–planet Systems

Cited by 69 publications

References 67 publications

Tidal dissipation in rotating low-mass stars and implications for the orbital evolution of close-in planets

Tidal dissipation in rotating low-mass stars and implications for the orbital evolution of close-in planets

MOVES III. Simultaneous X-ray and ultraviolet observations unveiling the variable environment of the hot Jupiter HD 189733b

The Fate of Close-in Planets: Tidal or Magnetic Migration?

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