Probing the terminator region atmosphere of the Hot-Jupiter XO-1b with transmission spectroscopy

TL;DR

This study presents the first infrared transmission spectrum of the hot-Jupiter XO-1b, revealing key atmospheric molecules and comparing its atmospheric composition with that of similar exoplanets, using Hubble Space Telescope data.

Contribution

First infrared spectrum of XO-1b's atmosphere obtained with NICMOS, identifying water vapor, methane, and carbon dioxide, and comparing it with other hot Jupiters.

Findings

Detection of H2O, CH4, CO2 in XO-1b's atmosphere

Spectral similarity between XO-1b and HD 209458b

Compatibility of NICMOS data with IRAC secondary transit measurements

Abstract

We report here the first infrared spectrum of the hot-Jupiter XO-1b. The observations were obtained with NICMOS instrument onboard the Hubble Space Telescope during a primary eclipse of the XO-1 system. Near photon-noise-limited spectroscopy between 1.2 and 1.8 micron allows us to determine the main composition of this hot-Jupiter's planetary atmosphere with good precision. This is the third hot-Jupiter's atmosphere for which spectroscopic data are available in the near IR. The spectrum shows the presence of water vapor (H2O), methane (CH4) and carbon dioxide (CO2), and suggests the possible presence of carbon monoxide (CO). We show that the published IRAC secondary transit emission photometric data are compatible with the atmospheric composition at the terminator determined from the NICMOS spectrum, with a range of possible mixing-ratios and thermal profiles; additional emission spectroscopy data are needed to reduce the degeneracy of the possible solutions. Finally, we note the similarity between the 1.2-1.8 micron transmission spectra of XO-1b and HD 209458b, suggesting that in addition to having similar stellar/orbital and planetary parameters the two systems may also have a similar exoplanetary atmospheric composition.