Deciphering the atmosphere of HAT-P-12b: solving discrepant results

TL;DR

This study resolves conflicting previous results on HAT-P-12b's atmosphere by identifying orbital parameter differences as the cause of discrepancies, leading to a consistent transmission spectrum with a slight spectral slope and possible potassium detection.

Contribution

It demonstrates that orbital parameter variations can cause spectral discrepancies and provides a homogeneous reanalysis to unify previous findings on HAT-P-12b's atmosphere.

Findings

Discrepancies were due to differing orbital parameters.

Homogeneous reanalysis yields a consistent spectrum.

Detected a low-amplitude spectral slope and tentative potassium absorption.

Abstract

Two independent investigations of the atmosphere of the hot Jupiter HAT-P-12b by two different groups resulted in discrepant solutions. Using broad-band photometry from the ground, one study found a flat and featureless transmission spectrum which was interpreted as a gray absorption by dense cloud coverage. The second study made use of the Hubble Space Telescope (HST) observations and found Rayleigh scattering at optical wavelengths caused by haze. The main purpose of this work is to find the source of this inconsistency and provide feedback to prevent similar discrepancies in future analyses of other exoplanetary atmospheres. We studied the observed discrepancy via two methods. With further broad-band observations in the optical wavelength regions, we strengthened the previous measurements in precision and with a homogeneous reanalysis of the published data, we managed to assess the systematic errors and the independent analyses of the two different groups. Repeating the analysis steps of both works, we found that deviating values for the orbital parameters are the reason for the aforementioned discrepancy. Our work showed a degeneracy of the planetary spectral slope with these parameters. In a homogeneous reanalysis of all data, the two literature data sets and the new observations converge to a consistent transmission spectrum, showing a low-amplitude spectral slope and a tentative detection of potassium absorption.