Very wide companion fraction from Gaia DR2: a weak or no enhancement for hot jupiter hosts, and a strong enhancement for contact binaries

TL;DR

This study investigates the prevalence of very wide companions around hot jupiter hosts and contact binaries using Gaia DR2 data, revealing a strong association for contact binaries but a weak or no enhancement for hot jupiter hosts, informing planetary and binary formation theories.

Contribution

It provides the first large-scale comparison of very wide companion fractions for hot jupiter hosts and contact binaries, highlighting different environmental influences on their formation.

Findings

Contact binaries have a 3.1 times higher wide companion fraction than field stars.

Hot jupiter hosts show only a weak or no significant increase in wide companion fraction.

Dual hot jupiter systems and dual contact binaries may be more common than random expectations.

Abstract

There is an ongoing debate on whether hot jupiter hosts are more likely to be found in wide binaries with separations of $\gtrsim 100$ AU. In this paper, we search for comoving, very wide companions with separations of $10^3-10^4$ AU for hot jupiter hosts and main-sequence contact binaries in Gaia DR2, and compare the very wide companion fractions with their object-by-object-matched field star samples. We find that $11.9\pm 2.5$% of hot jupiter hosts and $14.1\pm 1.0$% of contact binaries have companions at separations of $10^3-10^4$ AU. While the very wide companion fraction of hot jupiter hosts is a factor of $1.9\pm0.5$ larger than their matched field star sample, it is consistent, within $\sim1\sigma$, with that of matched field stars if the matching is only with field stars without close companions (within $\sim50$ AU) as is the case for hot jupiter hosts. The very wide companion fraction of contact binaries is a factor of $3.1\pm0.5$ larger than their matched field star sample, suggesting that the formation and evolution of contact binaries are either tied to or correlated with the presence of wide companions. In contrast, the weak enhancement of very wide companion fraction for hot jupiter hosts implies that the formation of hot jupiters is not as sensitive to those environment properties. Our results also hint that the occurrence rates of dual hot jupiter hosts and dual contact binaries may be higher than the expected values from random pairing of field stars, which may be due to their underlying metallicity and age dependence.