Revisiting the atmosphere of HAT-P-70b with CARMENES high-resolution transmission spectroscopy

TL;DR

This paper investigates the atmosphere of the ultra-hot Jupiter HAT-P-70 b using high-resolution transmission spectroscopy with CARMENES. By combining single-line measurements and cross-correlation with synthetic templates, the study confirms Ha, Na I, and Ca II signatures, places an upper limit on He, and reports a new tentative K I detection, while revealing Ca II and Fe I via cross-correlation with blue-shifted winds. The analysis suggests that Ha detections are more common around younger host stars and that UHJs with Ca II often also show Fe I, implying linked atmospheric chemistry or detectability. The results advance wind- and composition-focused constraints for UHJs around young stars and benchmark the relationship between age, evaporation, and refractory metal content in extreme exoplanetary atmospheres.

Abstract

Owing to hot and inflated envelopes that facilitate atmospheric studies, ultra-hot Jupiters (UHJs) have attracted much attention. Significant progress has been achieved, from enlarging the sample size to broadening the studies to encompass diverse stellar types and ages. Here, we present a transmission spectroscopy study of HAT-P-70b, an UHJ orbiting a young A-type star, through high-resolution observations with CARMENES at the 3.5m Calar Alto telescope. By using the line-by-line technique, we confirm the previous detections of Ha, Na I, and Ca II, report a new tentative detection of K I, and impose an upper limit on the He triplet absorption. Through cross-correlation analysis, we identify the Ca II and Fe I absorptions, both blue-shifted by approximately 5 km/s, indicating a day-to-night side atmospheric wind. Additionally, we find a new tentative detection of K I. We do not see any significant atmospheric molecular signal in the near-infrared data. Putting HAT-P-70b in the context of UHJs from the literature, it turns out that (1) Ha absorption is more common on gas giants orbiting stars younger than 1 Gyr, with a relative detection probability of $P_{\rm Age<1\,Gyr}({\rm Ha})/P_{\rm Age\geq1\,Gyr}({\rm Ha})\sim 3$; (2) any UHJ is likely to exhibit Fe I absorption if it has Ca II.

Figures (15)

• Figure 1: The S/N of the spectra (red) near the Na i$\lambda\lambda$5891,5898 $\text{\normalfont\AA}$ doublet lines and the airmass (blue) as a function of planet phase. Two vertical black dashed lines mark the first and fourth contacts of the transit event. The first three spectra (black crosses) are discarded due to their low S/N.
• Figure 2: The model of the RM and CLV (see Section \ref{['single_line_analysis']}) around the Na i doublet, normalized by the out-of-transit model spectrum, in the stellar rest frame. The horizontal red dashed lines mark the first and fourth contacts of the transit event. The black tilted dashed line represents the trace of the planetary orbital motion.
• Figure 3: Top panel: The raw spectrum matrix around the Na i doublet. Middle panel: The normalized spectrum matrix after pre-processing (see Section \ref{['spec_pre_processing']} for details). Bottom panel: The spectrum matrix after five SYSREM iterations. In all panels, the horizontal red dashed lines represent the first and fourth contacts of the transit event.
• Figure 4: Residual maps and transmission spectra around H$\alpha$ (left) and the He i NIR triplet (right) lines. Top panels: Residual maps in the stellar rest frame. The time since mid-transit time ($T_c$) is shown on the vertical axis, wavelength is on the horizontal axis, and relative absorption is color-coded. Dashed blue horizontal lines indicate the transit duration. Dashed cyan tilted lines show the theoretical trace of the planetary signals. Bottom panels: Transmission spectra obtained combining all the spectra between the first and fourth contacts. We show the original data in light gray and the data binned by 0.2 Å in black. The best Gaussian fit model is shown in red along with its $1\sigma$ uncertainties (shaded red region). Dashed cyan vertical lines indicate the H$\alpha$ (left) and the He i triplet (right) lines positions. All wavelengths in this figure are given in vacuum.
• Figure 4: Non-detections of 10 molecular species from the cross-correlation analyses. The left panel shows the cross-correlation S/N as a function of $K_p$ and $\Delta v$ while the right panel presents the 1D cross-correlation function at the literature $K_p$. The complete figure set (10 plots) is available in the online journal.