Orbital and Evolutionary Constraints on the Planet Hosting Binary GJ 86 from the Hubble Space Telescope

TL;DR

This study uses Hubble Space Telescope observations to characterize the binary system GJ 86, revealing a white dwarf companion and constraining the planet's mass, with implications for planet formation in similar systems.

Contribution

First detailed analysis of GJ 86 binary system with HST, identifying the white dwarf companion and refining planetary and orbital parameters.

Findings

The binary's semimajor axis is larger than 28 AU.

The white dwarf has a temperature of 8180 K and a mass of 0.59 solar masses.

The planet GJ 86Ab has a mass between 4.4 and 4.7 Jupiter masses.

Abstract

This paper presents new observations of the planet-hosting, visual binary GJ 86 (HR 637) using the Hubble Space Telescope. Ultraviolet and optical imaging with WFC3 confirms the stellar companion is a degenerate star and indicates the binary semimajor axis is larger than previous estimates, with a > 28 AU. Optical STIS spectroscopy of the secondary reveals a helium-rich white dwarf with C2 absorption bands and Teff = 8180 K, thus making the binary system rather similar to Procyon. Based on the 10.8 pc distance, the companion has 0.59 Msun and descended from a main-sequence A star of 1.9 Msun with an original orbital separation a > 14 AU. If the giant planet is coplanar with the binary, the mass of GJ 86Ab is between 4.4 and 4.7 MJup. The similarity of GJ 86 and Procyon prompted a re-analysis of the white dwarf in the latter system, with the tentative conclusion that Procyon hosts a planetesimal population. The periastron distance in Procyon is 20% smaller than in alpha Cen AB, but the metal-enriched atmosphere of Procyon B indicates that the planet formation process minimally attained 25 km bodies, if not small planets as in alpha Cen.