INCITE · mItigating stellar magNetic activity Contamination in Transmission spEctroscopy

Transmission spectroscopy (TS) is a technique, which measures the wavelength-dependent radius of a planet as it transits its star. From this, information about the chemical composition of a planet’s atmosphere can be obtained. The observed transmission spectrum is a combination of the planet and its host star. Inhomogeneities caused by spots and faculae present on stellar surfaces cause temporal changes in the observed transmission spectrum, mimicking a planet’s signal. It is crucial to understand the imprints of faculae and spots on TS to mitigate their signals. Modelling of stellar activity is challenging, and interpreting the stellar signal is full of degeneracies. The community is eager to overcome the stellar contamination conundrum, for which INCITE will propose solutions. INCITE’s objective is to build a methodology for stellar activity mitigation by physically modelling stellar activity in contemporaneous multiple-technique observations. As stellar activity models rely on the knowledge of the surface distribution of magnetic features and their respective brightness spectra, INCITE will combine recent efforts in these areas. The only star for which simultaneous observations of both the distribution of spots and faculae as well as multi-technique observations are available is the Sun. Therefore the first step within INCITE is to accurately model Sun-as-star observables. Another star presents itself as in ideal testbed. GJ 1214 is a cool , small, star, for which observations in multi-techniques, together with observations in TS by NASA’s JWST are available. Based on those two stars, stellar activity indicators that will allow for the most accurate mitigation of stellar activity in TS will be identified. Additionally, extensive studies will be conducted on how different configurations of magnetic fields will affect those activity indices and the mitigation in TS. This makes INCITE a proof-of concept study highly anticipated by the community.