High-resolution Imaging of Transiting Extrasolar Planetary systems (HITEP)

Abstract

Context. The formation and dynamical history of hot Jupiters is currently debated, with wide stellar binaries having been suggested as a potential formation pathway. Additionally, contaminating light from both binary companions and unassociated stars can significantly bias the results of planet characterisation studies, but can be corrected for if the properties of the contaminating star are known. Aim. We search for binary companions to known transiting exoplanet host stars, in order to determine the multiplicity properties of hot Jupiter host stars. We also search for and characterise unassociated stars along the line of sight, allowing photometric and spectroscopic observations of the planetary system to be corrected for contaminating light. Methods. We analyse lucky imaging observations of 97 Southern hemisphere exoplanet host stars, using the Two Colour Instrument on the Danish 1.54 m telescope. For each detected companion star, we determine flux ratios relative to the planet host star in two passbands, and measure the relative position of the companion. The probability of each companion being physically associated was determined using our two-colour photometry. Results. A catalogue of close companion stars is presented, including flux ratios, position measurements, and estimated companion star temperature. For companions that are potential binary companions, we review archival and catalogue data for further evidence. For WASP-77AB and WASP-85AB, we combine our data with historical measurements to determine the binary orbits, showing them to be moderately eccentric and inclined to the line of sight (and hence planetary orbital axis). Combining our survey with the similar Friends of Hot Jupiters survey, we conclude that known hot Jupiter host stars show a deficit of high mass stellar companions compared to the field star population; however, this may be a result of the biases in detection and target selection by ground-based surveys.

VIBES: Visual Binary Exoplanet survey with SPHERE

“…This enhancement can be caused by the secondary inducing spiral density waves in the protoplanetary disc, which can potentially stimulate gravitational instability (GI) (Batygin et al 2011;Rafikov 2013). This is in line with observations that suggest a 3-fold increase in hot Jupiter occurrence in binary stars compared to singles (Wang et al 2015;Ngo et al 2016;Evans et al 2018;Fontanive et al 2019). Binary stars should thus be taken into consideration when analysing planet formation and evolution, not only because binary stars represent ∼ 1/3 of stars in the Milky Way (M: 26.8% ± 1.4% Winters et al (2019), FGK: 33% ± 2% Raghavan et al (2010), A: 32.1 +3.9 −3.5 % De Rosa et al (2014)), but also to understand the robustness and diversity of planet formation.…”

A multiplicity study of transiting exoplanet host stars

“…Evans et al (2016a) carried out an additional high-resolution imaging campaign, and they determined a common proper motion with 2σ significance. An additional companion to the system that was also detected by Evans et al (2016a) was ruled out at a later stage and identified as an instrumental artefact (Evans et al 2018). Therefore, previous studies have presented much evidence that HAT-P-41 is indeed a binary system.…”

“…0950, which is unfortunately outside the IRDIS field of view. The potential companion, however, was picked up by Gaia DR2, and together with two additional sources listed that were previously considered unlikely to be bound by Evans et al (2018), these three objects were clearly proven to be background based on their parallaxes.…”

A multiplicity study of transiting exoplanet host stars

“…WASP-70 is the system with the second-brightest nearby companion, with ∆K = 1.38 ± 0.18 mag and a separation of 3.2 . The companion was detected in the discovery paper of the system (Anderson et al 2014) and in subsequent Lucky Imaging (Wöllert & Brandner 2015;Ginski et al 2016;Evans et al 2018) and adaptive-optics (Ngo et al 2016) studies. In Paper I we established that its proper motion is consistent with it being a bound, not background, object.…”