We present a python package ldtk that automates the calculation of custom stellar limb-darkening (LD) profiles and model-specific limb-darkening coefficients using the library of phoenix-generated specific intensity spectra by Husser et al. The aim of the package is to facilitate analyses requiring custom generated LD profiles, such as the studies of exoplanet transits – especially transmission spectroscopy, where the transit modelling is carried out for custom narrow passbands – eclipsing binaries, interferometry, and microlensing events. First, ldtk can be used to compute custom LD profiles with uncertainties propagated from the uncertainties in the stellar parameter estimates. Secondly, ldtk can be used to estimate the LD-model-specific coefficients with uncertainties for the most common LD models. Thirdly, ldtk can be directly integrated into the log posterior computation of any pre-existing modelling code with minimal modifications. The last approach can be used to constrain the LD model parameter space directly by the LD profile, allowing for the marginalization over the LD parameter space without the need to approximate the constraint from the LD profile using a prior.

We present TRICERATOPS, a new Bayesian tool that can be used to vet and validate TESS Objects of Interest (TOIs). We test the tool on 68 TOIs that have been previously confirmed as planets or rejected as astrophysical false positives. By looking in the false-positive probability (FPP)−nearby false-positive probability (NFPP) plane, we define criteria that TOIs must meet to be classified as validated planets (FPP < 0.015 and NFPP < 10⁻³), likely planets (FPP < 0.5 and NFPP < 10⁻³), and likely nearby false positives (NFPP > 10⁻¹). We apply this procedure on 384 unclassified TOIs and statistically validate 12, classify 125 as likely planets, and classify 52 as likely nearby false positives. Of the 12 statistically validated planets, 9 are newly validated. TRICERATOPS is currently the only TESS vetting and validation tool that models transits from nearby contaminant stars in addition to the target star. We therefore encourage use of this tool to prioritize follow-up observations that confirm bona fide planets and identify false positives originating from nearby stars.

We present a fast and user friendly exoplanet transit light-curve modelling package pytransit, implementing optimized versions of the Giménez and Mandel & Agol transit models. The package offers an object-oriented python interface to access the two models implemented natively in fortran with OpenMP parallelization. A partial OpenCL version of the quadratic Mandel–Agol model is also included for GPU-accelerated computations. The aim of pytransit is to facilitate the analysis of photometric time series of exoplanet transits consisting of hundreds of thousands of data points, and of multipassband transit light curves from spectrophotometric observations, as a part of a researcher's programming toolkit for building complex, problem-specific analyses.

We present k2sc (K2 Systematics Correction), a python pipeline to model instrumental systematics and astrophysical variability in light curves from the K2 mission. k2sc uses Gaussian Process regression to model position-dependent systematics and time-dependent variability simultaneously, enabling the user to remove both (e.g. for transit searches) or to remove systematics while preserving variability (for variability studies). For periodic variables, k2sc automatically computes estimates of the period, amplitude and evolution time-scale of the variability. We apply k2sc to publicly available K2 data from Campaigns 3–5 showing that we obtain photometric precision approaching that of the original Kepler mission. We compare our results to other publicly available K2 pipelines, showing that we obtain similar or better results, on average. We use transit injection and recovery tests to evaluate the impact of k2sc on planetary transit searches in K2 Pre-search Data Conditioning data, for planet-to-star radius ratios down to R_p/R_* = 0.01 and periods up to P = 40 d, and show that k2sc significantly improves the ability to distinguish between true and false detections, particularly for small planets. k2sc can be run automatically on many light curves, or manually tailored for specific objects such as pulsating stars or large amplitude eclipsing binaries. It can be run on ASCII and FITS light-curve files, regardless of their origin. Both the code and the processed light curves are publicly available, and we provide instructions for downloading and using them. The methodology used by k2sc will be applicable to future transit search missions such as TESS and PLATO.

Ultra-hot Jupiters orbit very close to their host star and consequently receive strong irradiation, causing their atmospheric chemistry to be different from the common gas giants. Here, we have studied the atmosphere of one of these particular hot planets, MASCARA-2b/KELT-20b, using four transit observations with high resolution spectroscopy facilities. Three of these observations were performed with HARPS-N and one with CARMENES. Additionally, we simultaneously observed one of the transits with MuSCAT2 to monitor possible spots in the stellar surface. At high resolution, the transmission residuals show the effects of Rossiter-McLaughlin and centre-to-limb variations from the stellar lines profiles, which we have corrected to finally extract the transmission spectra of the planet. We clearly observe the absorption features of CaII, FeII, NaI, Hα, and Hβ in the atmosphere of MASCARA-2b, and indications of Hγ and MgI at low signal-to-noise ratio. In the case of NaI, the true absorption is difficult to disentangle from the strong telluric and interstellar contamination. The results obtained with CARMENES and HARPS-N are consistent, measuring an Hα absorption depth of 0.68 ± 0.05 and 0.59 ± 0.07%, and NaI absorption of 0.11 ± 0.04 and 0.09 ± 0.05% for a 0.75 Å passband, in the two instruments respectively. The Hα absorption corresponds to ~1.2 R_p, which implies an expanded atmosphere, as a result of the gas heating caused by the irradiation received from the host star. For Hβ and Hγ only HARPS-N covers this wavelength range, measuring an absorption depth of 0.28 ± 0.06 and 0.21 ± 0.07%, respectively. For CaII, only CARMENES covers this wavelength range measuring an absorption depth of 0.28 ± 0.05, 0.41 ± 0.05 and 0.27 ± 0.06% for CaII λ8498Å, λ8542Å and λ8662Å lines, respectively. Three additional absorption lines of FeII are observed in the transmission spectrum by HARPS-N (partially covered by CARMENES), measuring an average absorption depth of 0.08 ± 0.04% (0.75 Å passband). The results presented here are consistent with theoretical models of ultra-hot Jupiters atmospheres, suggesting the emergence of an ionised gas on the day-side of such planets. Calcium and iron, together with other elements, are expected to be singly ionised at these temperatures and be more numerous than its neutral state. The Calcium triplet lines are detected here for the first time in transmission in an exoplanet atmosphere.