High-contrast Imaging around a 2 Myr-old CI Tau with a Close-in Gas Giant

TL;DR

This study used high-contrast imaging to search for outer companions around the 2-million-year-old star CI Tau, finding no such companions beyond 30 au and constraining the planet formation and migration history of its hot Jupiter.

Contribution

First high-contrast imaging search around CI Tau that constrains the presence of outer companions and informs planet migration scenarios.

Findings

No outer companions beyond ~30 au detected.

Outer gaps do not contain planets ≥2-4 M_Jup.

Results support Type II migration for CI Tau b.

Abstract

Giant planets around young stars serve as a clue to unveiling their formation history and orbital evolution. CI Tau is a 2\,Myr-old classical T-Tauri star hosting an eccentric hot Jupiter, CI Tau\,b. The standard formation scenario of a hot Jupiter predicts that planets formed further out and migrated inward. A high eccentricity of CI Tau b may be suggestive of high-$e$ migration due to secular gravitational perturbations by an outer companion. Also, ALMA 1.3\,mm-continuum observations show that CI Tau has at least three annular gaps in which unseen planets may exist. We present high-contrast imaging around CI Tau taken from Keck/NIRC2 $L^{\prime}$-band filter and vortex coronagraph that allows us to search for an outer companion. We did not detect any outer companion around CI Tau from angular differential imaging (ADI) using two deep imaging data sets. The detection limits from ADI-reduced images rule out the existence of an outer companion beyond $\sim30$\,au that can cause the Kozai-Lidov migration of CI Tau\,b. Our results suggest that CI Tau\,b may have experienced Type II migration from $\lesssim 2$\,au in Myrs. We also confirm that no planets with $\geq 2-4\,M_\mathrm{Jup}$ are hidden in two outer gaps.