High-resolution spectroscopic atmospheric studies of 5 hot Jupiters across the edge of the Neptune desert

Abstract

Hot Jupiters (HJs), especially the Ultra-Hot Jupiters (UHJs), are ideal targets for robust atmospheric characterization, thanks to their high equilibrium temperatures and large atmospheric scale heights, which result from their proximity to their host stars and intense stellar irradiation. Here, we present atmospheric studies of five planets, namely WASP-50b, WASP-117b, WASP-156b, WASP-167b, and WASP-173Ab. These five planets include two UHJs, two classic HJs, and one hot Neptune, with four of them just on the upper and middle borders of the Neptune desert, providing an interesting sample for investigating the connection between planetary atmospheric composition and bulk properties. We have not detected any significant absorption signals exceeding 3$σ$ in the three less-inflated, relatively high-density HJs (WASP-50b, WASP-156b, and WASP-173Ab). We marginally detect H$α$ and Li I with 3.2$σ$ and 3.1$σ$ in WASP-117b, respectively. In WASP-167b, we report tentative detection of H$α$ and Fe I at 4.6$σ$ and $\sim3.4σ$, receptively. In addition, Fe I is significantly detected with a max SNR of 7.3 $σ$ using the cross-correlation technique, which exhibits a blue-shifted signal. For WASP-167b, we perform an atmospheric retrieval and yield the abundances of Fe, Mg, Ca, Ti, V, and equilibrium temperature of ${2479^{+193}_{-174}}$K. Comparing WASP-173Ab and WASP-167b, both are UHJ, but with quite different extents of atmospheric signals, we propose that there may be a transition in $T_{\rm eq}$ between 1900 and 2300K.

Figures (15)

• Figure 1: The distribution of all known planets in the planetary mass against orbit period diagram (top panel) and planetary surface gravity against planet equilibrium temperature ($T_{\rm eq}$) diagram (bottom panel), respectively. The five planets in this study are marked with different shapes and colors for clarity. Notably, $T_{\rm eq}$ of our sample planet spans from $\sim$1000 K to $\sim$2300 K. The arrows in the top panel represent the $T_{\rm eq}$ increasing direction.
• Figure 2: Top panel: The RV curve produced by the spectrograph instrument for different targets: WASP-117 (a,b), WASP-156 (c), and WASP-173A (d), showing the RM effect and Kepler motion with green solid circles and error bars. The best-fit model using the rmfit procedure is shown in the solid red line, the orange shaded region indicates the 1$\sigma$, 2$\sigma$ and 3$\sigma$ models. Bottom panel: The residuals after removing the model prediction from the RV data.
• Figure 3: An example of telluric correction using Molecfit in the observed spectrum of WASP-173A b for Na i D1 $\&$ D2 (Top) and H i (Bottom). The observed spectra are shown in blue, while the spectra after telluric correction are shown in orange. The dashed green vertical lines represent the static positions of the atomic lines in vacuum.
• Figure 4: Top panel: The model of RM and CLV effects overplotted in solid red lines on the final transmission spectra which is shown in solid grey lines as background around the Na doublet lines, the binned transmission spectrum with error bar and a size of 0.1 Å is shown in black points. Bottom panel: The residuals after removing the model of RM and CLV effects.
• Figure 5: The Fourier transform of result after performing cross-correlation with Fe for WASP-167 b. The CLV and RM effects are characterized by the feature from the bottom-left to the top-right, the stellar pulsations are seen as the feature aligned with horizontal axis extending from the bottom-right to the top-left.