Transit spectroscopy of K2-33b with subaru/IRD: Spin-Orbit alignment and tentative atmospheric helium

• DOI: 10.1093/mnras/stae998
• Publication Date: 2024-04-18T00:29:52Z
• Authors: Teruyuki Hirano; Eric Gaidos; Hiroki Harakawa; Klaus W Hodapp; Takayuki Kotani; Tomoyuki Kudo; Takashi Kurokawa; Masayuki Kuzuhara; Andrew W Mann; Jun Nishikawa; Masashi Omiya; Takuma Serizawa; Motohide Tamura; Pa Chia Thao; Akitoshi Ueda; Sebastien Vievard
• Keywords: Radial velocity; Hot Jupiter; Super-Earth

ABSTRACT Exoplanets in their infancy are ideal targets to probe the formation and evolution history of planetary systems, including planet migration atmospheric dissipation. In this paper, we present spectroscopic observations analyses two transits K2-33b, which is known be one youngest transiting planets (age ≈ 8–11 Myr) around a pre-main-sequence M-type star. Analysing K2-33’s near-infrared spectra obtained by IRD instrument on Subaru, investigate spin-orbit angle transit-induced excess absorption for K2-33b. We attempt both classical modelling Rossiter–McLaughlin (RM) effect Doppler-shadow measurements projected stellar obliquity, finding low $\lambda =-6_{-58}^{+61}$ deg (for RM analysis) =-10_{-24}^{+22}$ analysis). effect, allow planet-to-star radius ratio float freely take into account possible smaller near infrared, but constraint obtain ($R_p/R_s=0.037_{-0.017}^{+0.013}$) inconclusive due radial-velocity precision. Comparison K2-33 1083 nm triplet metastable ortho-He I out 2021 transit reveal that could an escaping He-rich atmosphere. Under certain conditions mass XUV emission, implied escape rate sufficient remove Earth-mass H/He ∼1 Gyr, transforming object from Neptune super-Earth.