ExoTiC-ISM: A Python package for marginalised exoplanet transit parameters across a grid of systematic instrument models

TL;DR

ExoTiC-ISM is a Python package that performs marginalisation over systematic instrument models to accurately calibrate exoplanet transit light curves, improving the reliability of atmospheric composition analysis.

Contribution

It introduces a modular Python tool for systematic grid marginalisation in transit spectroscopy, applicable to current and future space telescope instruments.

Findings

Provides a systematic grid for HST WFC3 G141 and G102 detectors.

Enables robust transmission spectra through marginalisation.

Designed for extension to JWST instruments.

Abstract

To address the the problem of calibration of instrument systematics in transit light curves, we present the Python package ExoTiC-ISM. Transit spectroscopy can reveal many different chemical components in exoplanet atmospheres, but such results depend on well-calibrated transit light curve observations. Each transit data set will contain instrument systematics that depend on the instrument used and will need to be calibrated out with an instrument systematic model. The proposed solution in Wakeford et al. (2016) (arXiv:1601.02587 [astro-ph.EP]) is to use a marginalisation across a grid of systematic models in order to retrieve marginalised transit parameters. Doing this over observations in multiple wavelengths yields a robust transmission spectrum of an exoplanet. ExoTiC-ISM provides tools to perform this analysis, and its current capability contains a systematic grid that is applicable to the Wide Field Camera 3 (WFC3) detector on the Hubble Space Telescope (HST), particularly for the two infrared grisms G141 and G102. By modularisation of the code and implementation of more systematic grids, ExoTiC-ISM can be used for other instruments, and an implementation for select detectors on the James Webb Space Telescope (JWST) will provide robust transit spectra in the future.