Star-planet interactions. IV. Possibility of detecting the orbit-shrinking of a planet around a red giant

Abstract

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${}_{\odot }$ 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 $\sim$40 years before the planet engulfment. During this phase, the reflex motion of the star is between 660 and 710 m s${}^{-1}$. The spin period of the star increases by more than about 10 minutes per year in the last 3000 y before engulfment. During this period, the spin period of the star is shorter than 0.7 year. During this same period, the variation in orbital period, which is shorter than 0.18 year, 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{\it } changes of the beginning or end of the transit. A space mission like PLATO might be of great interest for detecting planets that are on the verge of being engulfed by red giants.

arXiv comment4 pages, 4 figures

References in corpus (17)

• Tidal Decay of Close Planetary Orbits
• The Orbital Evolution of Gas Giant Planets around Giant Stars
• The accretion of planets and brown dwarfs by giant stars -- II. solar mass stars on the red giant branch
• Foretellings of Ragnarök: World-engulfing Asymptotic Giants and the Inheritance of White Dwarfs
• Hot Jupiters and Cool Stars
• Can Planets survive Stellar Evolution?
• On the Orbits of Low-mass Companions to White Dwarfs and the Fates of the Known Exoplanets
• The Accretion of Brown Dwarfs and Planets by Giant Stars -- I. AGB Stars
• Departure from the constant-period ephemeris for the transiting exoplanet WASP-12 b
• Planet Engulfment by ~1.5-3 Solar-Mass Red Giants
• Tides and Tidal Engulfment in Post-Main Sequence Binaries: Period Gaps for Planets and Brown Dwarfs Around White Dwarfs
• The Role of Planet Accretion in Creating the Next Generation of Red Giant Rapid Rotators
• Star-planet interactions: II. Is planet engulfment the origin of fast rotating red giants?
• Planetary Companions to Evolved Intermediate-Mass Stars: 14 Andromedae, 81 Ceti, 6 Lyncis, and HD 167042
• Star-planet interactions: I. Stellar rotation and planetary orbits
• Evaporation of Jupiter like planets orbiting extreme horizontal branch stars
• TAPAS IV. TYC 3667-1280-1 b - the most massive red giant star hosting a warm Jupiter

Cited by in corpus (11)

• Star-planet interactions. V. Dynamical and equilibrium tides in convective zones
• Planetary Engulfment in the Hertzsprung--Russell Diagram
• Magnetic and tidal migration of close-in planets. Influence of secular evolution on their population
• Accounting for planet-shaped planetary nebulae
• Revisiting Kepler-444. II. Rotational, orbital and high-energy fluxes evolution of the system
• Star-planet interactions VI. Tides, stellar activity and planet evaporation
• Constraints on planetary tidal dissipation from a detailed study of Kepler 91b
• Coralie radial velocity search for companions around evolved stars (CASCADES) II. Seismic masses for three red giants orbited by long-period massive planets
• Revisiting Kepler-444 Part I. Seismic modelling and inversions of stellar structure
• Engulfment of a hot Jupiter as a possible origin of the rapid spin and internal spin misalignment of the planet-hosting red giant Kepler-56
• Jsolated Stars of Low Metallicity