The McDonald Accelerating Stars Survey: Architecture of the Ancient Five-planet Host System Kepler-444

We present the latest and most precise characterization of the architecture for the ancient (asymptotic to 11 Gyr) Kepler-444 system, which is composed of a K0 primary star (Kepler-444 A) hosting five transiting planets and a tight M-type spectroscopic binary (Kepler-444 BC) with an A-BC projected separation of 66 au. We have measured the system's relative astrometry using the adaptive optics imaging from Keck/NIRC2 and Kepler-444 A's radial velocities from the Hobby-Eberly Telescope and reanalyzed relative radial velocities between BC and A from Keck/HIRES. We also include the Hipparcos-Gaia astrometric acceleration and all published astrometry and radial velocities in an updated orbit analysis of BC's barycenter. These data greatly extend the time baseline of the monitoring and lead to significant updates to BC's barycentric orbit compared to previous work, including a larger semimajor axis (a = 52.2(-2.7)(+3.3)au), a smaller eccentricity (e = 0.55 +/- 0.05), and a more precise inclination (i = 85.degrees 4(-0.)degrees(+0.)(4)degrees(3)). We have also derived the first dynamical masses of B and C components. Our results suggest that Kepler-444 A's protoplanetary disk was likely truncated by BC to a radius of asymptotic to 8 au, which resolves the previously noticed tension between Kepler-444 A's disk mass and planet masses. Kepler-444 BC's barycentric orbit is likely aligned with those of A's five planets, which might be primordial or a consequence of dynamical evolution. The Kepler-444 system demonstrates that compact multiplanet systems residing in hierarchical stellar triples can form at early epochs of the universe and survive their secular evolution throughout cosmic time.

Automated summary

We present a precise characterization of the ancient Kepler-444 system, consisting of a primary star hosting five planets and a tight binary. Our measurements using adaptive optics imaging and radial velocities suggest a more accurate orbital analysis and new dynamical masses for the binary components. The system's dynamics indicate that compact multiplanet systems in hierarchical stellar triples can form and survive early epochs of the universe.