Near-IR transmission spectrum of HAT-P-32 b using HST/WFC3

TL;DR

This study analyzes the near-infrared transmission spectrum of the hot-Jupiter HAT-P-32b using HST/WFC3, comparing parametric and non-parametric methods, and employs Bayesian retrieval to infer atmospheric composition.

Contribution

It introduces a comparative analysis of parametric and ICA methods for transit spectrum extraction and applies Bayesian retrieval to characterize HAT-P-32b's atmosphere.

Findings

Consistent spectra within 0.5σ from different methods.

ICA provides more conservative error estimates, larger by 1.6-1.8 times.

Atmosphere likely contains water vapor and clouds.

Abstract

We report here the analysis of the near-infrared transit spectrum of the hot-Jupiter HAT-P-32b which was recorded with the Wide Field Camera 3 (WFC3) on-board the Hubble Space Telescope (HST). HAT-P-32b is one of the most inflated exoplanets discovered, making it an excellent candidate for transit spectroscopic measurements. To obtain the transit spectrum, we have adopted different analysis methods, both parametric and non parametric (Independent Component Analysis, ICA), and compared the results. The final spectra are all consistent within 0.5$\sigma$. The uncertainties obtained with ICA are larger than those obtained with the parametric method by a factor $\sim$1.6 - 1.8. This difference is the trade-off for higher objectivity due to the lack of any assumption about the instrument systematics compared to the parametric approach. The ICA error-bars are therefore worst-case estimates. To interpret the spectrum of HAT-P-32b, we used T-Rex, our fully Bayesian spectral retrieval code. As for other hot-Jupiters, the results are consistent with the presence of water vapor ($\log{\text{H}_2\text{O}} = -3.45_{-1.65}^{+1.83}$), clouds (top pressure between 5.16 and 1.73 bar). Spectroscopic data over a broader wavelength range will be needed to de-correlate the mixing ratio of water vapor from clouds and identify other possible molecular species in the atmosphere of HAT-P-32b.