Abstract
Abstract We explore the impact of outer stellar companions on the occurrence rate of giant planets detected with radial velocities. We searched for stellar and planetary companions to a volume-limited sample of solar-type stars within 25 pc. Using adaptive optics imaging observations from the Lick 3 m and Palomar 200″ Telescopes, we characterized the multiplicity of our sample stars, down to the bottom of the main sequence. With these data, we confirm field star multiplicity statistics from previous surveys. We additionally combined three decades of radial velocity (RV) data from the California Planet Search with newly collected RV data from Keck/HIRES and the Automated Planet Finder/Levy Spectrometer to search for planetary companions in these same systems. Using an updated catalog of both stellar and planetary companions, as well as detailed injection/recovery tests to determine our sensitivity and completeness, we measured the occurrence rate of planets among the single- and multiple-star systems. We found that planets with masses in the range of 0.1–10 M J and with semimajor axes of 0.1–10 au have an occurrence rate of planets per star when they orbit single stars and an occurrence rate of 0.12 ± 0.04 planets per star when they orbit a star in a binary system. Breaking the sample down by the binary separation, we found that only one planet-hosting binary system had a binary separation <100 au, and none had a separation <50 au. These numbers yielded planet occurrence rates of planets per star for binaries with separation a B > 100 au and planets per star for binaries with separation a B < 100 au. The similarity in the planet occurrence rate around single stars and wide primaries implies that wide binary systems should actually host more planets than single-star systems, since they have more potential host stars. We estimated a system-wide planet occurrence rate of 0.3 planets per wide binary system for binaries with separations a B > 100 au. Finally, we found evidence that giant planets in binary systems have a different semimajor-axis distribution than their counterparts in single-star systems. The planets in the single-star sample had a significantly higher occurrence rate outside of 1 au than inside 1 au by nearly 4σ, in line with expectations that giant planets are most common near the snow line. However, the planets in the wide binary systems did not follow this distribution, but rather had equivalent occurrence rates interior and exterior to 1 au. This may point to binary-mediated planet migration acting on our sample, even in binaries wider than 100 au.
Highlights
Half of all solar-type stars have at least one stellar or brown dwarf companion (Raghavan et al 2010), and planets around G- and K-type stars appear to be quite common (Batalha 2014)
Using the PyKLIP package of Wang et al (2015b), we modeled and subtracted the pointspread function (PSF) of each image based on a reference differential imaging library composed of the science frames of all other stars observed on the same night as the target frame
Based on our observations and the occurrence rates we have determined, we have found evidence that planet formation proceeds in the same way around each member of a wide binary as it does around a single star
Summary
Half of all solar-type stars have at least one stellar or brown dwarf companion (Raghavan et al 2010), and planets around G- and K-type stars appear to be quite common (Batalha 2014). Stellar multiplicity may impact planet formation and evolution in many ways. Simulations of planets in orbits around one member of a binary pair indicate that dynamically stable orbits can exist at semimajor axes within a few tenths of the binary separation, depending on the binary mass ratio and eccentricity (Holman & Wiegert 1999; Quintana et al 2007). Simulations indicate that even very widely spaced stellar companions can perturb the orbits of planets, causing migration and possible ejection from the system (Kaib et al 2013). Stellar companions may truncate protoplanetary disks, limiting planet formation in binary systems (Jang-Condell et al 2008)
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