HIP 67522 is known to host one of the youngest hot Jupiters, with an estimated age of 20 Myr. Such young planets are thought to retain primordial information about their orbital configurations and atmospheric properties, providing valuable insights into the formation and evolutionary history of close-in planets. We conducted transit spectroscopy of HIP 67522b using the InfraRed Doppler (IRD) instrument, a near-infrared high-resolution spectrograph (R 70, 000) mounted on the 8. 2 m Subaru Telescope. Our aim was to measure the spin-orbit angle via the Rossiter-McLaughlin effect and to probe the extended helium atmosphere at the 1083 nm line. Our observations covered two partial transits of HIP 67522b and revealed that (1) the planetary orbit is well aligned with the stellar spin axis (the projected obliquity of = 11−₂₂^+21 deg), and (2) the planet possesses a significantly extended helium atmosphere, indicative of strong atmospheric escape. The transit light curve at the helium line cannot be explained by a uniform, spherically symmetric atmospheric model, suggesting the presence of a non-uniform and/or non-spherical structure, such as a stream-like outflow. In this poster, we present the results of our analyses using several different atmospheric models.
Hirano et al. (Mon,) studied this question.
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