Evidence of Water Vapor in the Atmosphere of a Metal-Rich Hot Saturn with High-Resolution Transmission Spectroscopy

Abstract

Transmission spectroscopy presents one of the most successful approaches for investigating the atmospheres of exoplanets. We analyzed the near-infrared high-resolution transmission spectrum of a hot Saturn, HD 149026 b, taken using CARMENES spectrograph ($\mathcal{R}\sim 80,400$). We found evidence of H${}_2$O at an S/N of $\sim$4.8. We also performed grid search using a Bayesian framework and constrained the orbital velocity $K_{\mathrm{p}}$ and rest velocity $V_{\mathrm{rest}}$ to $158.17_{-7.90}^{+8.31}$ ${\mathrm{km}\mathrm{s}}^{-1}$ and $2.57_{-0.57}^{+0.54}$ ${\mathrm{km}\mathrm{s}}^{-1}$, respectively. Whilst the retrieved $K_{\mathrm{p}}$ value is consistent with theoretical prediction, the retrieved $V_{\mathrm{rest}}$ value is highly red-shifted ($>$3-$\ddot{I}ƒ$). This might be an indication of either anomalous atmospheric dynamics at play or an orbit with non-zero eccentricity. Additionally, we searched for HCN but no successful detection has been made possibly due to the relatively low S/N dataset. The detection of H${}_2$O and subsequent abundance retrieval, coupled with analysis of other species such as CO at the $K$-band, for example, might help us to get some information about the atmospheric C/O ratio and metallicity, which in turn could give us some insight into the planet formation scenario.

22 pages, 15 figures, 1 table. Accepted for publication at AJ