Know The Star, Know the Planet. IV. A Stellar Companion to the Host star of the Eccentric Exoplanet HD 8673b

TL;DR

This study confirms a faint stellar companion to HD 8673, an exoplanet host, and characterizes its properties, suggesting it influences the planet's highly eccentric orbit.

Contribution

The paper provides new observational data confirming and characterizing a stellar companion to HD 8673, refining its orbit and mass, and discussing its impact on the exoplanet's orbit.

Findings

The stellar companion is an early M dwarf with 0.33-0.45 M?

Projected separation of the companion is about 10 AU

Orbital parameters are constrained to semi-major axis 35-60 AU, eccentricity ? 0.5

Abstract

HD 8673 hosts a massive exoplanet in a highly eccentric orbit (e=0.723). Based on two epochs of speckle interferometry a previous publication identified a candidate stellar companion. We observed HD 8673 multiple times with the 10 m Keck II telescope, the 5 m Hale telescope, the 3.63 m AEOS telescope and the 1.5m Palomar telescope in a variety of filters with the aim of confirming and characterizing the stellar companion. We did not detect the candidate companion, which we now conclude was a false detection, but we did detect a fainter companion. We collected astrometry and photometry of the companion on six epochs in a variety of filters. The measured differential photometry enabled us to determine that the companion is an early M dwarf with a mass estimate of 0.33-0.45 M?. The companion has a projected separation of 10 AU, which is one of the smallest projected separations of an exoplanet host binary system. Based on the limited astrometry collected, we are able to constrain the orbit of the stellar companion to a semi-major axis of 35{60 AU, an eccentricity ? 0.5 and an inclination of 75{85?. The stellar companion has likely strongly in uenced the orbit of the exoplanet and quite possibly explains its high eccentricity.