Effects of Thermal Emission on the Transmission Spectra of Hot Jupiters

The atmosphere on the dayside of a highly irradiated close-in gas giant (also known as a hot Jupiter) absorbs a significant part of the incident stellar radiation, which again gets re-emitted in the infrared wavelengths both from the day and the night sides of the planet. The re-emitted thermal radiation from the nightside facing the observers during the transit event of such a planet contributes to the transmitted stellar radiation. We demonstrate that the transit spectra at the infrared region get altered significantly when such re-emitted thermal radiation of the planet is included. We assess the effects of the thermal emission of the hot Jupiters on the transit spectra by simulating observational spectroscopic data with corresponding errors from the different channels of the upcoming James Webb Space Telescope. We find that the effect is statistically significant with respect to the noise levels of those simulated data. Hence, we convey the important message that the planetary thermal re-emission must be taken into consideration in the retrieval models of transit spectra for hot Jupiters for a more accurate interpretation of the observed transit spectra.