2024AJ....168..106R

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 (${ \mathcal R }\sim \text{80,400}$). We found evidence of H₂O at a signal-to-noise ratio (S/N) of ∼4.8. We also performed grid search using a Bayesian framework and constrained the orbital velocity K_p and rest velocity V_rest to ${158.17}_{-7.90}^{+8.31}$ km s^–1 and ${2.57}_{-0.57}^{+0.54}$ km s^–1, respectively. While the retrieved K_p value is consistent with theoretical prediction, the retrieved V_rest value is highly redshifted (>3σ). This might be an indication of either anomalous atmospheric dynamics at play or an orbit with nonzero eccentricity. Additionally, we searched for HCN but no successful detection has been made, possibly due to the relatively low-S/N data set. The detection of H₂O and subsequent retrieval of its abundance, coupled with analysis of other species such as CO in 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's formation scenario.