KELT-9 b’s Asymmetric TESS Transit Caused by Rapid Stellar Rotation and Spin–Orbit Misalignment

ABSTRACT In close binary stars, the tidal excitation of pulsations typically dissipates energy, causing the system to evolve towards a circular orbit with aligned and synchronized stellar spins. However, for stars with self-excited pulsations, we demonstrate that tidal interaction with unstable pulsation modes can transfer energy in the opposite direction, forcing the spins of the stars away from synchronicity, and potentially pumping the eccentricity and spin–orbit misalignment angle. This ‘inverse’ tidal process only occurs when the tidally forced mode amplitude is comparable to the mode’s saturation amplitude, and it is thus most likely to occur in main-sequence gravity mode pulsators with orbital periods of a few days. We examine the long-term evolution of inverse tidal action, finding the stellar rotation rate can potentially be driven to a very large or very small value, while maintaining a large spin–orbit misalignment angle. Several recent asteroseismic analyses of pulsating stars in close binaries have revealed extremely slow core rotation periods, which we attribute to the action of inverse tides.

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Hint of curvature in the orbital motion of the exoplanet 51 Eridani b using 3 yr of VLT/SPHERE monitoring

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935031 ◽

2019 ◽

Vol 624 ◽

pp. A118 ◽

Cited By ~ 11

Author(s):

A.-L. Maire ◽

L. Rodet ◽

F. Cantalloube ◽

R. Galicher ◽

W. Brandner ◽

...

Keyword(s):

Orbital Motion ◽

Rotation Axis ◽

Spectral Energy Distribution ◽

Giant Planet ◽

Spectral Energy ◽

Spin Orbit ◽

Stellar Rotation ◽

Semi Major Axis ◽

Primary Star ◽

Orbital Parameters

Context. The 51 Eridani system harbors a complex architecture with its primary star forming a hierarchical system with the binary GJ 3305AB at a projected separation of 2000 au, a giant planet orbiting the primary star at 13 au, and a low-mass debris disk around the primary star with possible cold and warm components inferred from the spectral energy distribution. Aims. We aim to better constrain the orbital parameters of the known giant planet. Methods. We monitored the system over three years from 2015 to 2018 with the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument at the Very Large Telescope (VLT). Results. We measure an orbital motion for the planet of ~130 mas with a slightly decreasing separation (~10 mas) and find a hint of curvature. This potential curvature is further supported at 3σ significance when including literature Gemini Planet Imager (GPI) astrometry corrected for calibration systematics. Fits of the SPHERE and GPI data using three complementary approaches provide broadly similar results. The data suggest an orbital period of 32−9+17 yr (i.e., 12−2+4 au in semi-major axis), an inclination of 133−7+14 deg, an eccentricity of 0.45−0.15+0.10, and an argument of periastron passage of 87−30+34 deg [mod 180°]. The time at periastron passage and the longitude of node exhibit bimodal distributions because we do not yet detect whether the planet is accelerating or decelerating along its orbit. Given the inclinations of the orbit and of the stellar rotation axis (134–144°), we infer alignment or misalignment within 18° for the star–planet spin-orbit. Further astrometric monitoring in the next 3–4 yr is required to confirm at a higher significance the curvature in the motion of the planet, determine if the planet is accelerating or decelerating on its orbit, and further constrain its orbital parameters and the star–planet spin-orbit.

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Spin-orbit alignment and magnetic activity in the young planetary system AU Mic

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038695 ◽

2020 ◽

Vol 641 ◽

pp. L1 ◽

Cited By ~ 2

Author(s):

E. Martioli ◽

G. Hébrard ◽

C. Moutou ◽

J.-F. Donati ◽

É. Artigau ◽

...

Keyword(s):

Radial Velocity ◽

Template Matching ◽

Near Infrared ◽

Rotation Axis ◽

Magnetic Activity ◽

Radial Velocities ◽

Model Parameters ◽

Correlation Technique ◽

Spin Orbit ◽

Stellar Rotation

We present high-resolution near-infrared spectropolarimetric observations using the SPIRou instrument at Canada-France-Hawaii Telescope (CFHT) during a transit of the recently detected young planet AU Mic b, with supporting spectroscopic data from iSHELL at NASA InfraRed Telescope Facility. We detect Zeeman signatures in the Stokes V profiles and measure a mean longitudinal magnetic field of ¯Bℓ = 46.3 ± 0.7 G. Rotationally modulated magnetic spots likely cause long-term variations of the field with a slope of dBℓ/dt = −108.7 ± 7.7 G d−1. We apply the cross-correlation technique to measure line profiles and obtain radial velocities through CCF template matching. We find an empirical linear relationship between radial velocity and Bℓ, which allows us to estimate the radial-velocity induced by stellar activity through rotational modulation of spots for the five hours of continuous monitoring of AU Mic with SPIRou. We model the corrected radial velocities for the classical Rossiter-McLaughlin effect, using MCMC to sample the posterior distribution of the model parameters. This analysis shows that the orbit of AU Mic b is prograde and aligned with the stellar rotation axis with a sky-projected spin-orbit obliquity of λ = 0°−15°+18°. The aligned orbit of AU Mic b indicates that it formed in the protoplanetary disk that evolved into the current debris disk around AU Mic.

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