juliet: a versatile modelling tool for transiting and non-transiting exoplanetary systems

Abstract

Here we present juliet, a versatile tool for the analysis of transits, radial-velocities, or both. juliet is built over many available tools for the modelling of transits, radialvelocities and stochastic processes (here modelled as Gaussian Processes; GPs) in order to deliver a tool/wrapper which can be used for the analysis of transit photometry and radial-velocity measurements from multiple instruments at the same time, using nested sampling algorithms which allows it to not only perform a thorough sampling of the parameter space, but also to perform model comparison via bayesian evidences. In addition, juliet allows to fit transiting and non-transiting multi-planetary systems, and to fit GPs which might share hyperparameters between the photometry and radial-velocities simultaneously (e.g., stellar rotation periods), which might be useful for disentangling stellar activity in radial-velocity measurements. Nested Sampling, Importance Nested Sampling and Dynamic Nested Sampling is performed with publicly available codes which in turn give juliet multi-threading options, allowing it to scale the computing time of complicated multi-dimensional problems. We make juliet publicly available via GitHub.

Planetary system around the nearby M dwarf GJ 357 including a transiting, hot, Earth-sized planet optimal for atmospheric characterization

“…The Gaia G R P -band (630-1050 nm) and the TESS band (600-1000 nm) are very much alike, allowing us to estimate the dilution factor for TESS using Eq. 2in Espinoza et al (2018) to be D TESS = 0.996, which is consistent with 1.00, therefore compatible with no flux contamination.…”

“…We consider wide priors for B, C (log-uniform between 10 −5 ppm and 10 5 ppm), L (log-uniform between 10 −5 and 10 5 d), rotation period (uniform between 0 and 100 d), flux offsets (Gaussian centered on 0 and standard deviation of 10 5 ppm), and jitters (log-uniform between 1 and 10 5 ppm). The fit is performed using juliet (Espinoza et al 2018, see next section for a full description of the algorithm) and a close-up of the resulting fit is presented in Fig. 3 for illustration on how large the QP variations are in the WASP photometry, where the flux variability can be readily seen by eye.…”

TOI-150b and TOI-163b: two transiting hot Jupiters, one eccentric and one inflated, revealed by TESS near and at the edge of the JWST CVZ

“…For both TESS targets, a simultaneous analysis of the photometry, radial velocity, and stellar density was efficiently preformed using a new algorithm, juliet (Espinoza et al 2018), as applied in two other TESS discovery papers (Brahm et al 2018a;Espinoza et al 2019). juliet makes use of makes use of Nested Samplers using either MultiNest (Feroz et al 2009) via the PyMultiNest package (Buchner et al 2014) or the dynesty package (Speagle & Barbary 2018) in order to allow the computation of Bayesian model log-evidences, ln Z, useful for model comparison.…”

“…Because TESS has a large pixel size of 21" it is particularly important to search for nearby sources which could pollute the aperture requiring dilution factors (D) to be taken into account (see Sections 2.1 and 3.1.2 in Espinoza et al 2018). TOI-150 (Gaia DR2 5262709709389254528, G r p magnitude of 10.85) may face some obstacles with nearby neighbors, where there are two that have relatively low magnitudes (14.20, Gaia DR2 5262709881187945344, ∼41" ≈ 2 TESS pixels; 11.98, Gaia DR2 5262706681434867968, ∼62" ≈ 3 TESS pixels), and the other nearby targets are not significantly bright enough.…”

“…Because the Gaia G r p -band and the TESS band are quite similar, we can approximate what the dilution factor for TESS (D T ESS ) would be using equation 2 in Espinoza et al (2018) to get D ≈ 0.71 (assuming that the two bright objects are within the same TESS pixel). We therefore allow the TESS dilution factor to vary uniformly with the conservative lower bound of 0.5 to 1.0, with the idea in mind that the other targets are probably not impacting the flux significantly.…”