Friends of Hot Jupiters. Ii. No Correspondence Between Hot-Jupiter Spin-Orbit Misalignment and the Incidence of Directly Imaged Stellar Companions

Abstract

Multi-star systems are common, yet little is known about a stellar companion's influence on the formation and evolution of planetary systems. For instance, stellar companions may have facilitated the inward migration of hot Jupiters towards to their present day positions. Many observed short period gas giant planets also have orbits that are misaligned with respect to their star's spin axis, which has also been attributed to the presence of a massive outer companion on a non-coplanar orbit. We present the results of a multi-band direct imaging survey using Keck NIRC2 to measure the fraction of short period gas giant planets found in multi-star systems. Over three years, we completed a survey of 50 targets ("Friends of Hot Jupiters") with 27 targets showing some signature of multibody interaction (misaligned or eccentric orbits) and 23 targets in a control sample (well-aligned and circular orbits). We report the masses, projected separations, and confirmed common proper motion for the 19 stellar companions found around 17 stars. Correcting for survey incompleteness, we report companion fractions of 48% ± 9%, 47% ± 12%, and 51% ± 13% in our total, misaligned/eccentric, and control samples, respectively. This total stellar companion fraction is 2.8 σ larger than the fraction of field stars with companions approximately 50 − 2000 AU. We observe no correlation between misaligned/eccentric hot Jupiter systems and the incidence of stellar companions. Combining this result with our previous radial velocity survey, we determine that 72% ± 16% of hot Jupiters are part of multi-planet and/or multi-star systems.

The GTC exoplanet transit spectroscopy survey

“…We found that if we only fit the broadband measurements we arrive at similar values for HAT-P-32B's stellar parameters as the ones derived by Zhao et al (2014) and Ngo et al (2015). When including the optical data, however, the fit clearly favored cooler temperatures.…”

“…A.3 and A.4. It stands out that the K ′ band result of Ngo et al (2015) diverges significantly from all K S band values including their own. This offset is too large to be explained by the difference between the K ′ and K S band passes.…”

“…The optical companion was later confirmed to be bound to the HAT-P-32 system by Ngo et al (2015) from proper motion measurements and AO imaging. HAT-P-32B was further characterized as an M-dwarf by Zhao et al (2014) and Ngo et al (2015) who used near infrared broad band AO imaging to constrain its stellar parameters. Due to the close proximity of the two stars HAT-P-32A and B the flux of the latter was contributing to our measurements of the former.…”

“…A&A proofs: manuscript no. Nortmann_et_al_HAT-P-32b_arXiv_v1 Flux ratios between HAT-P-32B and HAT-P-32A obtained from infrared imaging in this work, Ngo15 (Ngo et al 2015), Zhao14 (Zhao et al 2014) and Adams13 (Adams et al 2013). (a) Value calculated from the relative magnitudes ∆mag given in the paper.…”

“…The planet's dayside temperature was measured to be T eq = 2042 ± 50 K by Zhao et al (2014) from secondary eclipse observations in the H, K S , 3.6 and 4.5 µm bands. An optically close companion was discovered in 2013 by Adams et al The stellar companion was recently studied in more detail and concluded to be an M-dwarf bound to the HAT-P-32 system from proper motion and AO measurements (Ngo et al 2015;Zhao et al 2014). Both studies place the effective temperature of the companion at about T eff ≈ 3500 K. Following the notation used in these works in the following we will refer to this stellar companion as HAT-P-32B and to the planet host star several other planet host stars for radial velocity (RV) trends that could indicate additional companions.…”