Obliquity measurement and atmospheric characterization of the WASP-74 planetary system

TL;DR

This study refines the orbital and atmospheric properties of the hot Jupiter WASP-74 b, measuring its obliquity as aligned with its host star's equator and analyzing its atmospheric absorption features.

Contribution

First measurement of WASP-74 b's obliquity and detailed atmospheric characterization using new high-resolution and multi-colour observations.

Findings

WASP-74 b's orbit is well-aligned with its star's equator (λ ≈ 0.77°).

No atomic spectral features detected in high-resolution transmission spectra.

Transmission spectrum shows a slope steeper than Rayleigh scattering predictions.

Abstract

We present new transit observations of the hot Jupiter WASP-74 b ($T_\mathrm{eq} \sim$ 1860 K) using the high-resolution spectrograph HARPS-N and the multi-colour simultaneous imager MuSCAT2. We refine the orbital properties of the planet and its host star, and measure its obliquity for the first time. The measured sky-projected angle between the stellar spin-axis and the planet's orbital axis is compatible with an orbit well-aligned with the equator of the host star ($\lambda = 0.77\pm0.99 \mathrm{deg}$). We are not able to detect any absorption feature of H$\alpha$, or any other atomic spectral features, in its high-resolution transmission spectra due to low S/N at the line cores. Despite previous claims regarding the presence of strong optical absorbers such TiO and VO gases in the atmosphere of WASP-74 b, the new ground-based photometry combined with a reanalysis of previously reported observations from the literature shows a slope in the low-resolution transmission spectrum steeper than expected from Rayleigh scattering alone.