Impact of Binary Stars on Planet Statistics -- I. Planet Occurrence Rates, Trends with Stellar Mass, and Wide Companions to Hot Jupiter Hosts

Abstract

Close binaries suppress the formation of circumstellar (S-type) planets and therefore significantly bias the inferred planet occurrence rates and statistical trends. After compiling various radial velocity and high-resolution imaging surveys, we determine that binaries with a 1 au fully suppress S-type planets, binaries with a ≈ 10 au host close planets at ≈ 15% the occurrence rate of single stars, and wide binaries with a 200 au have a negligible effect on planet formation. We show that F = 43% ± 6% of solar-type primaries do not host close planets due to suppression by close stellar companions. By removing spectroscopic binaries from their samples, radial velocity surveys for giant planets boost their detection rates by a factor of 1/(1-F ) = 1.8 ± 0.2 compared to transiting surveys. This selection bias fully accounts for the discrepancy in hot Jupiter occurrence rates inferred from these two detection methods. Correcting for both planet suppression by close binaries and transit dilution by wide binaries, the occurrence rate of small planets orbiting single G-dwarfs is 2.1 ± 0.3 times larger than the rate inferred from all G-dwarfs in the Kepler survey. About half (but not all) of the observed increase in small, short-period planets toward low-mass hosts can be explained by the corresponding decrease in the binary fraction. Finally, we demonstrate that the apparent enhancement of wide stellar companions to hot Jupiter hosts is due to multiple selection effects. Although very close binaries with secondary masses M 2 10 M J preferentially have wide tertiary companions, genuine hot Jupiters with M p ≈ 0.2 -4 M J that formed via core accretion do not exhibit a statistically significant excess of wide stellar companions.

The California Legacy Survey III. On The Shoulders of (Some) Giants: The Relationship between Inner Small Planets and Outer Massive Planets

“…Petigura et al (2018) analyzed the metallicity distribution of Kepler stars and planet hosts and found that warm sub-Neptune (1.7-4 R ⊕ ) occurrence is weakly correlated with host-star metallicity, doubling from -0.4 dex to +0.4 dex with ∼2σ significance. However, Moe & Kratter (2019) and Kutra & Wu (2020) later found that this correlation disappears if one decorrelates against the metallicity dependence of close binaries, which do not host short-period planets. This leaves open the possibility that the giant planets formed in metal-rich disks might directly facilitate small planet formation via their dynamical impact on the protoplanetary disk structure (e.g., Hasegawa & Pudritz 2011;Buchhave et al 2014).…”

The chaotic history of the retrograde multi-planet system in K2-290A driven by distant stars

“…As discussed by Hjorth et al (2021), K2-290 is the first system that provides strong support to the primordial disk misalignment theory (Batygin 2012;Lai 2014;Spalding & Batygin 2014). The companion star B lies at a desired distance of ∼ 100 au; not too close to suppress planet formation (Moe & Kratter 2019) and not too far to require unrealistically long disk lifetimes.…”

GTC/CanariCam deep mid-infrared imaging survey of northern stars within 5 pc

“…Several works have concluded that binarity has a minimal effect on overall planet frequency (Bonavita & Desidera 2007;Bergfors et al 2013;Piskorz et al 2015;Southworth et al 2020). On the other hand, some recent observational studies demonstrate an excess of wide stellar companions to stars which host high-mass hot Jupiters and brown dwarf companions on shortperiod orbits (Ngo et al 2016;Fontanive et al 2019;Moe & Kratter 2019;Fontanive & Bardalez Gagliuffi 2021). These conclude that certain types of binaries may support the proccess of formation of close-in highmass planetary and substellar companions.…”