Probing the extent of WASP-52 b's atmosphere. High-resolution observations and 3D modeling insights

TL;DR

This study probes the atmospheric escape of WASP-52 b by combining high-resolution He I 10833 Å observations with 3D Athena++ hydrodynamic simulations and a Cloudy NLTE radiative-transfer post-processing framework. The data suggest a not-strongly extended outflow, with an intermediate wind regime (approximate hydrodynamic escape parameter $\lambda_p\approx5$ and $T\approx9400$ K) that produces minimal line broadening and no detectable pre-/post-transit absorption. The 3D models reveal distinct morphologies (isotropic, anisotropic, torus, trailing tail), but all are broadly consistent with the non-detection of out-of-transit helium absorption; the ANISO scenario is disfavored by observed blueshift limits. The new radiative-transfer approach, which accounts for He$^{2+}$ formation and multiple species via Cloudy, enhances the ability to interpret low-density, extended outflows and can be applied to additional tracers across future observations, with all data and code publicly available.

Abstract

WASP-52 b is an inflated hot Jupiter with a large Roche lobe filling fraction, positioned in the hot Neptune desert. Previous in-transit observations of the helium triplet at 10833 A have reported a range of excess absorption values (1.5%-5.5%) and a lack of net blueshift relative to the planet's rest frame, distinguishing it from other escaping atmospheres. This study investigates the extent and morphology of material escaping from WASP-52 b, assessing whether its outflow resembles a stream-like structure, as suggested for HAT-P-67 b and HAT-P-32 b. We obtained high-resolution spectra with CRIRES+ and CARMENES, covering a broader orbital phase range ($\varphi \approx \pm0.1, \pm0.2, 0.5$) than previous studies. By analyzing the He I 10833 A line as a tracer of escape, we search for extended absorption beyond transit. Additionally, we explore possible outflow morphologies with three-dimensional (3D) hydrodynamic simulations, coupled with an improved radiative transfer approach, assessing the He I 10833 A triplet. The helium line shows no significant evidence of planetary material at the orbital phases observed in this work, though 3D modeling suggests such a structure could exist below observational detection limits. We conclude that the atmospheric outflow of WASP-52 b can be characterized by an intermediate hydrodynamic escape parameter, placing it in a transitional regime between cold outflows forming a stream-like morphology and hot outflows forming a tail. Additionally, the absence of a detectable in-transit blueshift in the helium line rules out a strong day-to-nightside anisotropy scenario.

Figures (11)

• Figure 1: Illustration (not to scale) of the observing strategy for the WASP-52 system. The planet orbits the central star counterclockwise, with different phase angles, $\varphi$, representing the observer's line of sight to the system in the orbital mid-plane. During negative phase angles (pre-transit), the observer probes a potential leading tail of escaping atmosphere, while positive phase angles (post-transit) could reveal additional absorption from a trailing tail. Observations were conducted during both pre- and post-transit phases to assess the extent of atmospheric escape. For an out-of-transit spectrum, where the planet’s atmospheric contribution is expected to be minimal, additional observations were taken near eclipse, when the planet is obscured by the star.
• Figure 2: Air mass (red) and signal-to-noise ratio (black) in the region of the Hei 10833 Å line ($10820.0~\text{\AA} < \lambda< 10870.1~\text{\AA}$) of the CRIRES$^+$ observations. Shaded regions indicate the start and end of the planet's transit and eclipse.
• Figure 3: Air mass and signal-to-noise ratios (S/N) of the CARMENES observations (combined spectra). Black triangles indicate the S/N in the region of the helium triplet ($10820.0$ Å$~< \lambda< 10870.1$ Å), while the gray squares represent the S/N in the region of the Hi 6565 Å line ($6550.0$ Å $< \lambda< 6580.0$ Å). The red dots show the air mass during the observation.
• Figure 4: Stellar Hei 10833 Å line observed with CARMENES (top), CRIRES$^+$ (middle), and the equivalent widths of the line core across orbital phases (bottom). Dashed lines in the top and middle panels indicate the vacuum wavelengths of the helium triplet, while solid lines mark the line core region used for EW calculations. Observations from this study (squares and dots in the bottom panel) show no significant variability in the stellar helium triplet. We interpret the data points as a baseline of spectra uncontaminated by planetary absorption, yielding a weighted mean EW of $(190.5 \pm 2.5)$ mÅ (green line). For reference, we include the estimated mid-transit equivalent width based on the observations by kirk_kecknirspec_2022, obtained by adding the reported planetary excess to the stellar baseline measured from our data.
• Figure 5: Density distribution of the planetary wind in the orbital mid-plane from the Athena++ 3D hydrodynamic simulations. The star is located at the center, with the planet on the left orbiting in the counterclockwise direction. The diagonal dotted lines represent the observing angles of various orbital phases $\varphi$. The dark dotted contours indicate surfaces with densities of $\rho = 1\times 10^{-18}$ g cm$^{-3}$.