TransitFit: an exoplanet transit fitting package for multi-telescope datasets and its application to WASP-127~b, WASP-91~b, and WASP-126~b

We present TransitFit, an open-source Python~3 package designed to fit exoplanetary transit light-curves for transmission spectroscopy studies (Available at https://github.com/joshjchayes/TransitFit and https://github.com/spearnet/TransitFit, with documentation at https://transitfit.readthedocs.io/). TransitFit employs nested sampling to offer efficient and robust multi-epoch, multi-wavelength fitting of transit data obtained from one or more telescopes. TransitFit allows per-telescope detrending to be performed simultaneously with parameter fitting, including the use of user-supplied detrending alogorithms. Host limb darkening can be fitted either independently ("uncoupled") for each filter or combined ("coupled") using prior conditioning from the PHOENIX stellar atmosphere models. For this TransitFit uses the Limb Darkening Toolkit (LDTk) together with filter profiles, including user-supplied filter profiles. We demonstrate the application of TransitFit in three different contexts. First, we model SPEARNET broadband optical data of the low-density hot-Neptune WASP-127~b. The data were obtained from a globally-distributed network of 0.5m--2.4m telescopes. We find clear improvement in our broadband results using the coupled mode over uncoupled mode, when compared against the higher spectral resolution GTC/OSIRIS transmission spectrum obtained by Chen et al. (2018). Using TransitFit, we fit 26 transit observations by TESS to recover improved ephemerides of the hot-Jupiter WASP-91~b and a transit depth determined to a precision of 170~ppm. Finally, we use TransitFit to conduct an investigation into the contested presence of TTV signatures in WASP-126~b using 126 transits observed by TESS, concluding that there is no statistically significant evidence for such signatures from observations spanning 31 TESS sectors.Comment: 14 pages, 5 figures, 5 tables, submitted to MNRAS. Temporary data address at https://cdsarc.u-strasbg.fr/ftp/vizier.submit/wasp-127b/ (Final address to be included in accepted paper

TransitFit: combined multi-instrument exoplanet transit fitting for JWST, HST and ground-based transmission spectroscopy studies

We present TRANSITFIT†, a package designed to fit exoplanetary transit light-curves. TRANSITFIT offers multi-epoch, multi-wavelength fitting of multi-telescope transit data. TRANSITFIT allows per-telescope detrending to be performed simultaneously with transit parameter fitting, including custom detrending. Host limb darkening can be fitted using prior conditioning from stellar atmosphere models. We demonstrate TRANSITFIT in a number of contexts. We model multi-telescope broadband optical data from the ground-based SPEARNET survey of the low-density hot-Neptune WASP-127 b and compare results to a previously published higher spectral resolution GTC/OSIRIS transmission spectrum. Using TRANSITFIT, we fit 26 transit epochs by TESS to recover improved ephemeris of the hot-Jupiter WASP-91 b and a transit depth determined to a precision of 111 ppm. We use TRANSITFIT to conduct an investigation into the contested presence of TTV signatures in WASP-126 b using 180 transits observed by TESS, concluding that there is no statistically significant evidence for such signatures from observations spanning 27 TESS sectors. We fit HST observations of WASP-43 b, demonstrating how TRANSITFIT can use custom detrending algorithms to remove complex baseline systematics. Lastly, we present a transmission spectrum of the atmosphere of WASP-96 b constructed from simultaneous fitting of JWST NIRISS Early Release Observations and archive HST WFC3 transit data. The transmission spectrum shows generally good correspondence between spectral features present in both datasets, despite very different detrending requirements

TransitFit: combined multi-instrument exoplanet transit fitting for JWST, HST, and ground-based transmission spectroscopy studies

We present TRANSITFIT1, a package designed to fit exoplanetary transit light curves. TRANSITFIT offers multi-epoch, multi-wavelength fitting of multi-telescope transit data. TRANSITFIT allows per-telescope detrending to be performed simultaneously with transit parameter fitting, including custom detrending. Host limb darkening can be fitted using prior conditioning from stellar atmosphere models. We demonstrate TRANSITFIT in a number of contexts. We model multi-telescope broad-band optical data from the ground-based SPEARNET survey of the low-density hot-Neptune WASP-127b and compare results to a previously published higher spectral resolution GTC/OSIRIS transmission spectrum. Using TRANSITFIT, we fit 26 transit epochs by TESS to recover improved ephemeris of the hot-Jupiter WASP-91b and a transit depth determined to a precision of 111 ppm. We use TRANSITFIT to conduct an investigation into the contested presence of TTV signatures in WASP-126b using 180 transits observed by TESS, concluding that there is no statistically significant evidence for such signatures from observations spanning 27 TESS sectors. We fit HST observations of WASP-43 b, demonstrating how TRANSITFIT can use custom detrending algorithms to remove complex baseline systematics. Lastly, we present a transmission spectrum of the atmosphere of WASP-96b constructed from simultaneous fitting of JWST NIRISS Early Release Observations and archive HST WFC3 transit data. The transmission spectrum shows generally good correspondence between spectral features present in both data sets, despite very different detrending requirements