The origin of the eccentricity of the hot Jupiter in CI Tau

TL;DR

This paper investigates the origin of the high eccentricity of the hot Jupiter in CI Tau, demonstrating that disc interactions or dynamical scattering could explain its current orbit within the system's age.

Contribution

It provides long-term simulations showing disc-induced eccentricity growth and explores dynamical scattering as an alternative origin for the planet's eccentricity.

Findings

Disc can excite eccentricity within < 1 Myr.

Eccentricity can be pumped even with low surface density.

Dynamical scattering can produce observed eccentricity.

Abstract

Following the recent discovery of the first radial velocity planet in a star still possessing a protoplanetary disc (CI Tau), we examine the origin of the planet's eccentricity (e $\sim 0.3$). We show through long timescale ($10^5$ orbits) simulations that the planetary eccentricity can be pumped by the disc, even when its local surface density is well below the threshold previously derived from short timescale integrations. We show that the disc may be able to excite the planet's orbital eccentricity in $<$ a Myr for the system parameters of CI Tau. We also perform two planet scattering experiments and show that alternatively the observed planet may plausibly have acquired its eccentricity through dynamical scattering of a migrating lower mass planet, which has either been ejected from the system or swallowed by the central star. In the latter case the present location and eccentricity of the observed planet can be recovered if it was previously stalled within the disc's magnetospheric cavity.