The orbits of the quadruple star system 88 Tau A from PHASES differential astrometry and radial velocity

TL;DR

This study combines high-precision astrometry and radial velocity data over 20 years to determine the detailed orbital architecture and component masses of the complex quadruple star system 88 Tau A, revealing non-coplanar sub-systems.

Contribution

First orbital solution for one short-period pair in 88 Tau A, with component masses, distance, and mutual inclinations determined from combined astrometry and radial velocities.

Findings

Component masses determined to a few percent accuracy.

First measurement of mutual orbital inclinations showing non-coplanarity.

Orbital parameters of the short-period pairs derived for the first time.

Abstract

We have used high precision differential astrometry from the Palomar High-precision Astrometric Search for Exoplanet Systems (PHASES) project and radial velocity measurements covering a time-span of 20 years to determine the orbital parameters of the 88 Tau A system. 88 Tau is a complex hierarchical multiple system comprising a total of six stars; we have studied the brightest 4, consisting of two short-period pairs orbiting each other with an 18-year period. We present the first orbital solution for one of the short-period pairs, and determine the masses of the components and distance to the system to the level of a few percent. In addition, our astrometric measurements allow us to make the first determination of the mutual inclinations of the orbits. We find that the sub-systems are not coplanar.