Star-planet interactions

Privitera, Giovanni; Meynet, Georges; Eggenberger, P.; Vidotto, A. A.; Villaver, E.; Bianda, M.

doi:10.1051/0004-6361/201528044

Cited by 59 publications

(58 citation statements)

References 45 publications

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“…We used computations performed by Privitera et al (2016b) that follow the evolution of the star and the evolution of the planetary orbit in a consistent way. By consistent, we mean here that the changes in orbit influence the stellar rotation through a boundary condition that allows angular momentum to be removed from or added to the star (depending on the sign of the tidal forces), and the change in planetary orbit accounts for the changes in the properties of the star (the tidal forces typically depend on the radius of the star and the size of the convective envelope, among other factors; see Eq.…”

Section: Stellar and Orbital Evolution Modelsmentioning

confidence: 99%

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Star-planet interactions

Meynet

Eggenberger

Privitera

et al. 2017

A&A

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The surface rotations of some red giants are so fast that they must have been spun up by tidal interaction with a close companion, either another star, a brown dwarf, or a planet. We focus here on the case of red giants that are spun up by tidal interaction with a planet. When the distance between the planet and the star decreases, the spin period of the star decreases, the orbital period of the planet decreases, and the reflex motion of the star increases. We study the change rate of these three quantities when the circular orbit of a planet of 15 M J that initially orbits a 2 M star at 1 au shrinks under the action of tidal forces during the red giant phase. We use stellar evolution models coupled with computations of the orbital evolution of the planet, which allows us to follow the exchanges of angular momentum between the star and the orbit in a consistent way. We obtain that the reflex motion of the red giant star increases by more than 1 m s −1 per year in the last ∼40 yr before the planet engulfment. During this phase, the reflex motion of the star is between 660 and 710 m s −1 . The spin period of the star increases by more than about 10 min per year in the last 3000 yr before engulfment. During this period, the spin period of the star is shorter than 0.7 yr. During this same period, the variation in orbital period, which is shorter than 0.18 yr, is on the same order of magnitude. Changes in reflex-motion and spin velocities are very small and thus most likely out of reach of being observed. The most promising way of detecting this effect is through observations of transiting planets, that is, through changes of the beginning or end of the transit. For the relatively long orbital periods expected around red giants, long observing runs of typically a few years are needed. Interesting star-planet systems that currently are in this stage of orbit-shrinking would be red giants with fast rotation (above typically 4−5 km s −1 ), a low surface gravity (log g lower than 2), and having a planet at a distance typically smaller than about 0.4−1 au, depending on log g. A space mission like PLATO might be of great interest for detecting planets that are on the verge of being engulfed by red giants. The discovery of a few systems, even only one, would provide very interesting clues about the physics of tidal interaction between a red giant and a planet.

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Section: Stellar and Orbital Evolution Modelsmentioning

confidence: 99%

“…In previous works, we studied the evolution of orbits of planets of different masses around stars of various initial masses and rotations with different orbital periods (Privitera et al 2016b). We determined the initial conditions required for an engulfment to occur during the red giant phase.…”

Section: Introductionmentioning

confidence: 99%

Star-planet interactions

Meynet

Eggenberger

Privitera

et al. 2017

A&A

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“…Such a star does not have a deep outer convective zone to maintain a powerful magnetic dynamo that would result in effective magnetic braking on the main sequence (cf. Privitera et al 2016a). Eventually this means more angular momentum conservation for the post-main sequence evolution, supporting the scenario of mixing up angular momentum.…”

Section: Summary and Discussionmentioning

confidence: 99%

Antisolar differential rotation with surface lithium enrichment on the single K-giant V1192 Orionis

Kővári

Strassmeier

Carroll

et al. 2017

A&A

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Context. Stars with about 1−2 solar masses at the red giant branch (RGB) represent an intriguing period of stellar evolution, i.e. when the convective envelope interacts with the fast-rotating core. During these mixing episodes freshly synthesized lithium can come up to the stellar surface along with high angular momentum material. This high angular momentum may alter the surface rotation pattern. Aims. The single rapidly rotating K-giant V1192 Ori is revisited to determine its surface differential rotation, lithium abundance, and basic stellar properties such as a precise rotation period. The aim is to independently verify the antisolar differential rotation of the star and possibly find a connection to the surface lithium abundance. Methods. We applied time-series Doppler imaging to a new multi-epoch data set. Altogether we reconstructed 11 Doppler images from spectroscopic data collected with the STELLA robotic telescope between 2007-2016. We used our inversion code iMap to reconstruct all stellar surface maps. We extracted the differential rotation from these images by tracing systematic spot migration as a function of stellar latitude from consecutive image cross-correlations. Results. The position of V1192 Ori in the Hertzsprung-Russell diagram suggests that the star is in the helium core-burning phase just leaving the RGB bump. We measure A(Li) NLTE = 1.27, i.e. a value close to the anticipated transition value of 1.5 from Li-normal to Li-rich giants. Doppler images reveal extended dark areas arranged quasi-evenly along an equatorial belt. No cool polar spot is found during the investigated epoch. Spot displacements clearly suggest antisolar surface differential rotation with α = −0.11 ± 0.02 shear coefficient. Conclusions. The surface Li enrichment and the peculiar surface rotation pattern may indicate a common origin.

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“…During the migration process, orbital angular momentum are transferred to stellar spin. Therefore, these red giant branch stars would present higher rotation rates, which could not be explained by any reasonable model for single star evolution [12,53]. From the observational sample of [54], [12,21,53] identified some fast rotating red giants that are candidates of having engulfed their planets in a recent past.…”

Section: Can Planets Influence the Activity Of Their Host Stars?mentioning

confidence: 98%

“…Therefore, these red giant branch stars would present higher rotation rates, which could not be explained by any reasonable model for single star evolution [12,53]. From the observational sample of [54], [12,21,53] identified some fast rotating red giants that are candidates of having engulfed their planets in a recent past. Since rotation and magnetic fields are closely related [20], [21] then further proposed, that these fast rotating red giants would also show a higher magnetic field.…”

Section: Can Planets Influence the Activity Of Their Host Stars?mentioning

confidence: 98%

Stellar magnetic activity and exoplanets

Vidotto¹

2017

EPJ Web Conf.

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Abstract. It has been proposed that magnetic activity could be enhanced due to interactions between close-in massive planets and their host stars. In this article, I present a brief overview of the connection between stellar magnetic activity and exoplanets. Stellar activity can be probed in chromospheric lines, coronal emission, surface spot coverage, etc. Since these are manifestations of stellar magnetism, these measurements are often used as proxies for the magnetic field of stars. Here, instead of focusing on the magnetic proxies, I overview some recent results of magnetic field measurements using spectropolarimetric observations. Firstly, I discuss the general trends found between large-scale magnetism, stellar rotation, and coronal emission and show that magnetism seems to be correlated to the internal structure of the star. Secondly, I overview some works that show evidence that exoplanets could (or not) act as to enhance the activity of their host stars.

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Star-planet interactions

Cited by 59 publications

References 45 publications

Star-planet interactions

Star-planet interactions

Antisolar differential rotation with surface lithium enrichment on the single K-giant V1192 Orionis

Stellar magnetic activity and exoplanets

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