Know the Star, Know the Planet. III. Discovery of Late-Type Companions to Two Exoplanet Host Stars
Lewis C. Roberts, Jr., Andrei Tokovinin, Brian D. Mason, Reed L., Riddle, William I. Hartkopf, Nicholas M. Law, and Christoph Baranec

TL;DR
This paper reports the discovery of stellar companions to two exoplanet host stars, HD 2638 and 30 Ari B, using adaptive optics imaging, revealing their potential influence on planetary systems.
Contribution
It provides the first confirmed stellar companions to these systems and analyzes their orbital properties and implications for exoplanet hosting in binary systems.
Findings
Both systems have new stellar companions within 30 AU.
HD 2638's companion has an estimated orbital period of 130 years.
30 Ari B's companion has an estimated orbital period of 80 years.
Abstract
We discuss two multiple star systems that host known exoplanets: HD 2638 and 30 Ari B. Adaptive optics imagery revealed an additional stellar companion to both stars. We collected multi-epoch images of the systems with Robo-AO and the PALM-3000 adaptive optics systems at Palomar Observatory and provide relative photometry and astrometry. The astrometry indicates that the companions share common proper motion with their respective primaries. Both of the new companions have projected separations less than 30 AU from the exoplanet host star. Using the projected separations to compute orbital periods of the new stellar companions, HD 2638 has a period of 130 yrs and 30 Ari B has a period of 80 years. Previous studies have shown that the true period is most likely within a factor of three of these estimated values. The additional component to the 30 Ari makes it the second confirmed…
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