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

Abstract

There is an ongoing debate on whether hot jupiter hosts are more likely to be found in wide binaries with separations of ≳ 100 AU. In this paper, we search for comoving, very wide companions with separations of 103 − 104 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 ± 2.5% of hot jupiter hosts and 14.1 ± 1.0% of contact binaries have companions at separations of 103 − 104 AU. While the very wide companion fraction of hot jupiter hosts is a factor of 1.9 ± 0.5 larger than their matched field star sample, it is consistent, within ∼1σ, with that of matched field stars if the matching is only with field stars without close companions (within ∼50 AU) as is the case for hot jupiter hosts. The very wide companion fraction of contact binaries is a factor of 3.1 ± 0.5 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.

Architecture of Hierarchical Stellar Systems and Their Formation

“…On the other hand, very close binaries prefer to be accompanied by other stars, rather than live alone. Hwang et al [26] found that 14.1 ± 1% of contact binaries have wide companions, while their fraction for all stars is 4.5%. They used the Gaia catalog and made a simplifying assumption that stars with variable fluxes are contact binaries (most of them are).…”

Architecture of Hierarchical Stellar Systems and their Formation

“…On the other hand, very close binaries prefer to be accompanied by other stars, rather than live alone. Hwang et al (2020) found that 14.1±1% of contact binaries have wide companions, while their fraction for all stars is 4.5%. They used the Gaia catalog and made a simplifying assumption that stars with variable fluxes are contact binaries (most of them are).…”

Enhancement of Double-Close-Binary Quadruples

“…Using the astrometric data from Gaia, we identify resolved comoving pairs of stars following a procedure similar to that described in Hwang et al (2020a). For each target star in the query, its nearby stars are selected from the parent sample (and thus they satisfy the same selection criteria described in Sec.…”

“…To remove contamination of comoving pairs in comoving groups and stellar clusters, we compute the parameter N comoving group, originally used in Hwang et al (2020a), for each star. This parameter is the number of stars in the parent sample which are, with respect to the target star: (1) between 10 5 AU and 10 6 AU away, and (2) have relative velocity < 10 km/s.…”

“…The resulting separations and relative velocities of all the pairs are shown in Figure 1, left. The solid line is the demarcation line proposed by Hwang et al (2020a) to select comoving pairs. Most of the pairs are chance-alignment pairs located above the demarcation line with high relative velocities and separations.…”