An internal heating mechanism operating in ultra-short-period planets orbiting magnetically active stars

Lanza, A. F.

doi:10.1051/0004-6361/202140284

Cited by 10 publications

(5 citation statements)

References 71 publications

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“…Finally, we note that the possibility of a close commensurability with the stellar rotation period being twice the orbital period may be relevant for the internal heating of ultra-shortperiod planets around very active young stars, as recently proposed by Lanza (2021).…”

Section: Discussionsupporting

confidence: 67%

A model for spin–orbit commensurability and synchronous starspot activity in stars with close-by planets

Lanza

2022

A&A

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Context. The rotation period of some planet-hosting stars appears to be in close commensurability with the orbital period of their close-by planets. In some cases, starspots rotating with a commensurable period have been detected, while the star displays latitudinal differential rotation. Aims. A model is proposed to interpret such a phenomenon based on the excitation of resonant oscillations in the interior magnetic field of the star by a component of the tidal potential with a very low frequency in the reference frame rotating with the star. Methods. A magnetic flux tube located in the overshoot layer of the star is assumed in order to study the excitation of the resonant oscillations in the magnetostrophic regime. The model considers a planet on a circular oblique orbit, and the growth timescale of the oscillations is estimated. To keep the system in resonance with the exciting potential despite the variations in the magnetic field or tidal frequency, a self-regulating mechanism is proposed. Results. The model is applied to ten systems and proves capable of accounting for the observed close commensurability in eight of them by assuming a magnetic field between 102 and 104 G. Systems with distant low-mass planets, such as AU Mic and HAT-P-11, cannot be interpreted by the proposed model. Conclusions. Consequences for the spin–orbit evolution of the systems, including the dynamical tides and gyrochronology of planet-hosting stars, are discussed together with the effects on the chromospheric features produced by star–planet magnetic interactions.

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Section: Discussionsupporting

confidence: 67%

A model for spin–orbit commensurability and synchronous starspot activity in stars with close-by planets

Lanza

2022

A&A

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“…Finally, we note that the possibility of a close commensurability with the stellar rotation period being twice the orbital period may be relevant for the internal heating of ultra-short period planets around very active young stars as recently proposed by Lanza (2021).…”

Section: Discussionsupporting

confidence: 62%

A model for spin-orbit commensurability and synchronous starspot activity in stars with close-by planets

Lanza

2022

Preprint

Self Cite

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Context. The rotation period of some planet-hosting stars appears to be in close commensurability with the orbital period of their close-by planets. In some cases, starspots rotating with a commensurable period have been detected, while the star displays latitudinal differential rotation. Aims. A model is proposed to interpret such a phenomenon based on the excitation of resonant oscillations in the interior magnetic field of the star by a component of the tidal potential with a very low frequency in the reference frame rotating with the star. Methods. A magnetic flux tube located in the overshoot layer of the star is assumed to study the excitation of the resonant oscillations in the magnetostrophic regime. The model considers a planet on a circular oblique orbit and the growth timescale of the oscillations is estimated. To keep the system in resonance with the exciting potential, in spite of the variations in the magnetic field or tidal frequency, a self-regulating mechanism is proposed.Results. The model is applied to ten systems and proves capable of accounting for the observed close commensurability in eight of them by assuming a magnetic field between 10 2 and 10 4 G. Systems with low-mass distant planets, such as AU Mic and HAT-P-11, cannot be interpreted by the proposed model. Conclusions. Consequences for the spin-orbit evolution of the systems, including dynamical tides and gyrochronology of planethosting stars, are discussed together with the effects on the chromospheric features produced by star-planet magnetic interactions.

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“…Despite this and the numerous theoretical models that describe SPI (e.g. Lanza 2018Lanza , 2021Lanza , 2022, the case of AU Mic remains unexplained.…”

Section: Light Curve Analysismentioning

confidence: 99%

Short term variability of DS Tuc A observed with TESS

Colombo,

Petralia,

Micela

2022

Preprint

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Context. Impulsive short term variations occur in all kinds of solar-type stars. They are the results of complex phenomena such as the stellar magnetic field reconnection, low-level variability or in some cases even star-planet interactions. The radiation arising from these events is often highly energetic and, in stars hosting planets, may interact with the planetary atmospheres. Studying the rate of these energetic phenomena is fundamental to understand their role in modifying the chemical composition or, in some extreme cases, to the disruption of the planetary atmospheres.Aims. Here, we present a new procedure developed to identify the impulsive events in TESS light curves. Our goal is to have a simple and effective tool to study the short-term activity of a star using only its light curve, in order to derive its distribution and energetic. As our first case, we studied the system DS Tuc. Methods. Our technique consists of fitting the TESS light curves using iteratively Gaussian processes in order to remove all the long-term stellar activity contributions. Then, we identify the impulsive events and, derive amplitudes, time scales and the amount of energy emitted. Results. We validate our procedure using the AU Mic TESS light curves obtaining results consistent with those presented in the literature. We estimate the frequency distribution of energetic events for DS Tuc. In particular, we find that there are ≈ 2 events per day with energy greater than 2 × 10 32 erg. We find evidence for a favoured stellar phase for short term activity on AU Mic, and also indications of short term activity in phase with the planetary orbit. For DS Tuc we find that the events distribution is not equally spaced in time but often grouped. The resulting distribution may be used to estimate the impact of short term variability on planetary atmosphere chemical compositions.

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An internal heating mechanism operating in ultra-short-period planets orbiting magnetically active stars

Cited by 10 publications

References 71 publications

A model for spin–orbit commensurability and synchronous starspot activity in stars with close-by planets

A model for spin–orbit commensurability and synchronous starspot activity in stars with close-by planets

A model for spin-orbit commensurability and synchronous starspot activity in stars with close-by planets

Short term variability of DS Tuc A observed with TESS

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