Influence of Stellar Multiplicity on Planet Formation. Ii. Planets Are Less Common in Multiple-Star Systems With Separations Smaller Than 1500 Au

Abstract

Almost half of the stellar systems in the solar neighborhood are made up of multiple stars. In multiple-star systems, planet formation is under the dynamical influence of stellar companions, and the planet occurrence rate is expected to be different from that for single stars. There have been numerous studies on the planet occurrence rate of single star systems. However, to fully understand planet formation, the planet occurrence rate in multiplestar systems needs to be addressed. In this work, we infer the planet occurrence rate in multiple-star systems by measuring the stellar multiplicity rate for planet host stars. For a sub-sample of 56 Kepler planet host stars, we use adaptive optics (AO) imaging and the radial velocity (RV) technique to search for stellar companions. The combination of these two techniques results in high search completeness for stellar companions. We detect 59 visual stellar companions to 25 planet host stars with AO data. Three stellar companions are within 2 ′′ , and 27 within 6 ′′ . We also detect 2 possible stellar companions (KOI 5 and KOI 69) showing long-term RV acceleration. After correcting for a bias against planet detection in multiple-star systems due to flux contamination, we find that planet formation is suppressed in multiple-star systems with separations smaller than 1500 AU. Specifically, we find that compared to single star systems, planets in multiple-star systems occur 4.5 ± 3.2, 2.6±1.0, and 1.7±0.5 times less frequently when a stellar companion is present at a distance of 10, 100, and 1000 AU, respectively. This conclusion applies only to circumstellar planets; the planet occurrence rate for circumbinary planets requires further investigation.

On the Occurrence Rate of Hot Jupiters in Different Stellar Environments

“…We consider these two cases separately. For gravitationally bound multiple stellar systems, the stellar multiplicity rate for planet host stars (Wang et al 2014a(Wang et al , 2014b) is significantly lower than that for the solar neighborhood (Raghavan et al 2010). We adopt the stellar multiplicity rate measured from Wang et al (2014a) for stellar separations smaller than 1000 AU, i.e., 24% ± 7%.…”

“…At these separations, there is no significant difference of stellar multiplicity between Wang et al (2014a) and Duquennoy & Mayor (1991). In addition, the result from Wang et al (2014a) beyond 1000 AU is prone to contamination of optical doubles and multiples, which will be addressed in the following section. In our simulation for gravitationally bound systems, the mass ratio of stellar companions to the primary star follows a normal distribution with a mean and standard deviation of 0.23 and 0.42 (Duquennoy & Mayor 1991).…”

“…For the Kepler mission, a planet is missed when the detection signal-to-noise ratio (S/N) is lower than 7.1 (Jenkins et al 2010). The S/N is calculated based on the following equation (Wang et al 2014a):…”

“…Beyond 1000 AU, we adopt the log-normal distribution of stellar separation from Duquennoy & Mayor (1991). At these separations, there is no significant difference of stellar multiplicity between Wang et al (2014a) and Duquennoy & Mayor (1991). In addition, the result from Wang et al (2014a) beyond 1000 AU is prone to contamination of optical doubles and multiples, which will be addressed in the following section.…”

THE APOGEE SPECTROSCOPIC SURVEY OFKEPLERPLANET HOSTS: FEASIBILITY, EFFICIENCY, AND FIRST RESULTS

“…Another method is to generate a large grid of synthetic EB blend scenarios and compare the models to the observed light curves via a χ 2 analysis (e.g., BLENDER, Torres et al 2011), although the technique can be computationally expensive and difficult to apply to all KPCs en masse. In addition, imaging surveys (e.g., Howell et al 2011;Adams et al 2012) can be used to inform the photometric analyses described above, particularly to identify fainter stars that exist within the light curve aperture, and to search for wide stellar companions to study any relationships between exoplanet properties and host star multiplicity (Wang et al 2014).…”