A multiplicity study of transiting exoplanet host stars

Abstract

Context. Binarity is a widespread phenomenon around solar-type stars, including the host stars of transiting extrasolar planets. Aims. We performed a detailed study of six transiting planetary systems with relatively bright stars close enough to affect observations of these systems. These contaminants were characterised in a companion work. Methods. We used theoretical spectra to propagate the observed K-band light ratios into the optical passbands used to observe these systems. Light curves were analysed whilst taking the contaminating light and its uncertainty into account. We present and applied a method to correct the velocity amplitudes of the host stars for the presence of contaminating light. Results. We determined the physical properties of six systems (WASP-20, WASP-70, WASP-8, WASP-76, WASP-2, and WASP-131) whilst accounting for contaminating light. In the case of WASP-20, the measured physical properties are very different for the three scenarios considered: ignoring binarity, planet transits brighter star, and planet transits fainter star. In the other five cases, our results are very similar to those obtained when neglecting contaminating light. We used our results to determine the mean correction factors to planet radius, ⟨XR⟩, mass, ⟨XM⟩, and density, ⟨Xρ⟩, caused by nearby objects. We find ⟨XR⟩ = 1.009 ± 0.045, which is smaller than literature values because we were able to reject the possibility that the planet orbits the fainter star in all but one case. We find ⟨XM⟩ = 1.031 ± 0.019, which is larger than ⟨XR⟩ because of the strength of the effect of contaminating light on the radial velocity measurements of the host star. We find ⟨Xρ⟩ = 0.995 ± 0.046: the small size of this correction is due to two effects: the corrections on planet radius and mass partially cancel; and some nearby stars are close enough to contaminate the light curves of the system but not radial velocities of the host star. These corrections can be applied to samples of transiting hot Jupiters to statistically remove biases due to light contamination. Conclusions. We conclude that binarity of planet host stars is important for the small number of transiting hot Jupiters with a very bright and close nearby star, but it has only a small effect on population-level studies of these objects.

ARES I: WASP-76 b, A Tale of Two HST Spectra*

“…Here we present an analysis of the transmission and emission spectra of WASP-76 b, taken with the WFC3 G141 grism aboard HST. Although not reported in the discovery paper (West et al 2016), the presence of a stellar companion was noted in several studies (Wöllert & Brandner 2015;Ginski et al 2016;Ngo et al 2016;Bohn et al 2020) and the common proper motion of the two objects was confirmed by Southworth et al (2020). This was not accounted for in previous WFC3 transmission studies and, using Wayne simulations (Varley et al 2017), we show that this companion affects the spectral data obtained.…”

“…The stellar companion of WASP-76, reported by Bohn et al (2020) and Southworth et al (2020) has a K magnitude which is ∼2.30 fainter and the separation between both stars is only 0 436. As such, it is expected to have contaminated the transmission and emission spectra obtained by Hubble.…”

The Census of Exoplanets in Visual Binaries: Population Trends from a Volume-Limited Gaia DR2 and Literature Search

“…We complemented the multiplicity data from these databases with the Catalogue of Exoplanets in Binary Star Systems 5 (Schwarz et al, 2016). We added to this all systems from published surveys searching for visual stellar companions to circumprimary planetary systems (Luhman and Jayawardhana, 2002;Patience et al, 2002;Udry et al, 2004;Mugrauer et al, 2006;Mugrauer et al, 2007a;Mugrauer et al, 2007b;Raghavan et al, 2006;, Eggenberger et al, 2011Daemgen et al, 2009;Mugrauer and Neuhäuser, 2009;Adams et al, 2012;Adams et al, 2013;Ginski et al, 2012, Ginski et al, 2016Ginski et al, 2020;Lillo-Box et al, 2012;Bergfors et al, 2013;Faedi et al, 2013;Lodieu et al, 2014;Wang et al, 2014;Mugrauer and Ginski, 2015;Wöllert et al, 2015;Deacon et al, 2016;Kraus et al, 2016;Ngo et al, 2016;Ngo et al, 2017;Furlan et al, 2017;Moutou et al, 2017;Coker et al, 2018;Dietrich and Ginski, 2018;Ziegler et al, 2018;Fontanive et al, 2019;Mugrauer, 2019;Bohn et al, 2020;Southworth et al, 2020) or reviews of planets in binaries (Bonavita and Desidera, 2007;Bonavita and Desidera, 2020;…”

More planetary candidates from K2 Campaign 5 using TRAN_K2

“…We also note that WASP-30b is not a planetary system, but a stellar binary, with a near main-sequence F8 primary and a 61 M J secondary, that can be classified as a brown dwarf. Because there is no mass entry in TIC for WASP-20, we relied on the analysis of Southworth et al (2020). WASP-20 is a binary, and the stellar parameters correspond to the brighter companion.…”