A SEA BASS on the exoplanet HD209458b

TL;DR

This paper applies the SEA BASS Bayesian analysis method to real datasets of exoplanet HD209458b, simultaneously deriving stellar limb-darkening profiles, transit depths, and planetary atmospheric transmission spectra across multiple wavelengths.

Contribution

It improves the SEA BASS algorithm with additional passbands and geometric parameters, demonstrating its effectiveness on Hubble data and measuring stellar limb-darkening and planetary transmission spectra.

Findings

Measured stellar limb-darkening profiles across 290-570 nm.

Successfully extracted the exoplanet's transmission spectrum.

Ruled out some theoretical limb-darkening models.

Abstract

We present here the first application of Stellar and Exoplanetary Atmospheres Bayesian Analysis Simultaneous Spectroscopy (SEA BASS) on real datasets. SEA BASS is a scheme that enables the simultaneous derivation of four-coefficient stellar limb-darkening profiles, transit depths, and orbital parameters from exoplanetary transits at multiple wavelengths. It relies on the wavelength-independence of the system geometry and on the reduced limb-darkening effect in the infrared. This approach has been introduced by Morello et al. (2017) (without the SEA BASS acronym), who discuss several tests on synthetic datasets. Here, we (1) improve on the original algorithm by using multiple Spitzer/InfraRed Array Camera passbands and a more effective set of geometric parameters, (2) demonstrate its ability with Hubble Space Telescope/Space Telescope Imaging Spectrograph datasets, by (3) measuring the HD209458 stellar limb-darkening profile over multiple passbands in the 290-570 nm range with sufficient precision to rule out some theoretical models that have been adopted previously in theliterature, and (4) simultaneously extracting the transmission spectrum of the exoplanet atmosphere. The higher photometric precision of the next-generation instruments, such as those onboard the James Webb Space Telescope, will enable modeling the star-planet systems with unprecedented detail, and increase the importance of SEA BASS for avoiding the potential biases introduced by inaccurate stellar limb-darkening models.